| 1. |
- Schweinsberg, Martin, et al.
(författare)
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Same data, different conclusions : Radical dispersion in empirical results when independent analysts operationalize and test the same hypothesis
- 2021
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Ingår i: Organizational Behavior and Human Decision Processes. - : Elsevier BV. - 0749-5978 .- 1095-9920. ; 165, s. 228-249
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Tidskriftsartikel (refereegranskat)abstract
- In this crowdsourced initiative, independent analysts used the same dataset to test two hypotheses regarding the effects of scientists' gender and professional status on verbosity during group meetings. Not only the analytic approach but also the operationalizations of key variables were left unconstrained and up to individual analysts. For instance, analysts could choose to operationalize status as job title, institutional ranking, citation counts, or some combination. To maximize transparency regarding the process by which analytic choices are made, the analysts used a platform we developed called DataExplained to justify both preferred and rejected analytic paths in real time. Analyses lacking sufficient detail, reproducible code, or with statistical errors were excluded, resulting in 29 analyses in the final sample. Researchers reported radically different analyses and dispersed empirical outcomes, in a number of cases obtaining significant effects in opposite directions for the same research question. A Boba multiverse analysis demonstrates that decisions about how to operationalize variables explain variability in outcomes above and beyond statistical choices (e.g., covariates). Subjective researcher decisions play a critical role in driving the reported empirical results, underscoring the need for open data, systematic robustness checks, and transparency regarding both analytic paths taken and not taken. Implications for orga-nizations and leaders, whose decision making relies in part on scientific findings, consulting reports, and internal analyses by data scientists, are discussed.
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| 2. |
- Weinstein, John N., et al.
(författare)
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The cancer genome atlas pan-cancer analysis project
- 2013
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 45:10, s. 1113-1120
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Tidskriftsartikel (refereegranskat)abstract
- The Cancer Genome Atlas (TCGA) Research Network has profiled and analyzed large numbers of human tumors to discover molecular aberrations at the DNA, RNA, protein and epigenetic levels. The resulting rich data provide a major opportunity to develop an integrated picture of commonalities, differences and emergent themes across tumor lineages. The Pan-Cancer initiative compares the first 12 tumor types profiled by TCGA. Analysis of the molecular aberrations and their functional roles across tumor types will teach us how to extend therapies effective in one cancer type to others with a similar genomic profile. © 2013 Nature America, Inc. All rights reserved.
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| 3. |
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| 4. |
- Greibe, Tine, 1974, et al.
(författare)
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Are "Pinholes" the Cause of Excess Current in Superconducting Tunnel Junctions? A Study of Andreev Current in Highly Resistive Junctions
- 2011
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 106:9
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Tidskriftsartikel (refereegranskat)abstract
- In highly resistive superconducting tunnel junctions, excess subgap current is usually observed and is often attributed to microscopic pinholes in the tunnel barrier. We have studied the subgap current in superconductor-insulator-superconductor (SIS) and superconductor-insulator-normal-metal ( SIN) junctions. In Al/AlOx/Al junctions, we observed a decrease of 2 orders of magnitude in the current upon the transition from the SIS to the SIN regime, where it then matched theory. In Al/AlOx/Cu junctions, we also observed generic features of coherent diffusive Andreev transport in a junction with a homogenous barrier. We use the quasiclassical Keldysh-Green function theory to quantify single- and two-particle tunneling and find good agreement with experiment over 2 orders of magnitude in transparency. We argue that our observations rule out pinholes as the origin of the excess current.
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| 5. |
- Greibe, Tine, 1974, et al.
(författare)
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Improvement of chip design to reduce resonances in subgap regime of Josephson junctions
- 2009
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 150, s. 052063-
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Konferensbidrag (refereegranskat)abstract
- Excess current peaks in the IV curves of SIS Josephson junctions have been observed by some groups [1–3]. These peaks have the shape of a resonance as a function of voltage. The resonances appear in the subgap regime of the junctions and the subgap current (leakage current) is concealed. The positions of the resonances do not change as a magnetic field is applied to the junctions, but their amplitude decreases when the supercurrent is suppressed. We have measured the subgap current of Al/AlOx/Al junctions and we show that these resonances are due to resonant modes in the chip design which are excited by the ac-Josephson effect. We present a chip design that decreases the amplitude of the resonances to a such degree that the subgap current is quantifiable.
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| 6. |
- Heid, Iris M, et al.
(författare)
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Meta-analysis identifies 13 new loci associated with waist-hip ratio and reveals sexual dimorphism in the genetic basis of fat distribution
- 2010
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 42:11, s. 949-960
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Tidskriftsartikel (refereegranskat)abstract
- Waist-hip ratio (WHR) is a measure of body fat distribution and a predictor of metabolic consequences independent of overall adiposity. WHR is heritable, but few genetic variants influencing this trait have been identified. We conducted a meta-analysis of 32 genome-wide association studies for WHR adjusted for body mass index (comprising up to 77,167 participants), following up 16 loci in an additional 29 studies (comprising up to 113,636 subjects). We identified 13 new loci in or near RSPO3, VEGFA, TBX15-WARS2, NFE2L3, GRB14, DNM3-PIGC, ITPR2-SSPN, LY86, HOXC13, ADAMTS9, ZNRF3-KREMEN1, NISCH-STAB1 and CPEB4 (P = 1.9 × 10⁻⁹ to P = 1.8 × 10⁻⁴⁰) and the known signal at LYPLAL1. Seven of these loci exhibited marked sexual dimorphism, all with a stronger effect on WHR in women than men (P for sex difference = 1.9 × 10⁻³ to P = 1.2 × 10⁻¹³). These findings provide evidence for multiple loci that modulate body fat distribution independent of overall adiposity and reveal strong gene-by-sex interactions.
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| 7. |
- Locke, Adam E, et al.
(författare)
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Genetic studies of body mass index yield new insights for obesity biology.
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 197-401
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Tidskriftsartikel (refereegranskat)abstract
- Obesity is heritable and predisposes to many diseases. To understand the genetic basis of obesity better, here we conduct a genome-wide association study and Metabochip meta-analysis of body mass index (BMI), a measure commonly used to define obesity and assess adiposity, in up to 339,224 individuals. This analysis identifies 97 BMI-associated loci (P < 5 × 10(-8)), 56 of which are novel. Five loci demonstrate clear evidence of several independent association signals, and many loci have significant effects on other metabolic phenotypes. The 97 loci account for ∼2.7% of BMI variation, and genome-wide estimates suggest that common variation accounts for >20% of BMI variation. Pathway analyses provide strong support for a role of the central nervous system in obesity susceptibility and implicate new genes and pathways, including those related to synaptic function, glutamate signalling, insulin secretion/action, energy metabolism, lipid biology and adipogenesis.
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| 8. |
- Nilsson, Henrik, et al.
(författare)
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A Radio Frequency Single-Electron Transistor Based on an InAs/InP Heterostructure Nanowire
- 2008
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 8:3, s. 872-875
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate radio frequency single-electron transistors fabricated from epitaxially grown InAs/InP heterostructure nanowires. Two sets of double-barrier wires with different barrier thicknesses were grown. The wires were suspended 15 nm above a metal gate electrode. Electrical measurements on a high-resistance nanowire showed regularly spaced Coulomb oscillations at a gate voltage from - 0.5 to at least 1.8 V. The charge sensitivity was measured to 32 mu e(rms) Hz (- 1/2) at 1.5 K. A low-resistance single-electron transistor showed regularly spaced oscillations only in a small gate-voltage region just before carrier depletion. This device had a charge sensitivity of 2.5 mu e(rms) Hz (- 1/2). At low frequencies this device showed a typical 1/f noise behavior, with a level extrapolated to 300 mu e(rms) Hz (- 1/2) at 10 Hz.
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| 9. |
- van de Vegte, Yordi, et al.
(författare)
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Genetic insights into resting heart rate and its role in cardiovascular disease
- 2023
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- The genetics and clinical consequences of resting heart rate (RHR) remain incompletely understood. Here, the authors discover new genetic variants associated with RHR and find that higher genetically predicted RHR decreases risk of atrial fibrillation and ischemic stroke. Resting heart rate is associated with cardiovascular diseases and mortality in observational and Mendelian randomization studies. The aims of this study are to extend the number of resting heart rate associated genetic variants and to obtain further insights in resting heart rate biology and its clinical consequences. A genome-wide meta-analysis of 100 studies in up to 835,465 individuals reveals 493 independent genetic variants in 352 loci, including 68 genetic variants outside previously identified resting heart rate associated loci. We prioritize 670 genes and in silico annotations point to their enrichment in cardiomyocytes and provide insights in their ECG signature. Two-sample Mendelian randomization analyses indicate that higher genetically predicted resting heart rate increases risk of dilated cardiomyopathy, but decreases risk of developing atrial fibrillation, ischemic stroke, and cardio-embolic stroke. We do not find evidence for a linear or non-linear genetic association between resting heart rate and all-cause mortality in contrast to our previous Mendelian randomization study. Systematic alteration of key differences between the current and previous Mendelian randomization study indicates that the most likely cause of the discrepancy between these studies arises from false positive findings in previous one-sample MR analyses caused by weak-instrument bias at lower P-value thresholds. The results extend our understanding of resting heart rate biology and give additional insights in its role in cardiovascular disease development.
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| 10. |
- Zeng, Lunjie, 1983, et al.
(författare)
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Direct observation of the thickness distribution of ultra thin AlOx barriers in Al/AlOx/Al Josephson junctions
- 2015
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 48:39
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Tidskriftsartikel (refereegranskat)abstract
- We have directly measured the thickness distribution of the tunnel barriers in state-of-the-art Al/AlOx/Al tunnel junctions. From the distribution we can conclude that less than 10% of the junction area dominates the electron tunnelling. The barriers have been studied by transmission electron microscopy, specifically using atomic resolution annular dark field (ADF) scanning transmission electron microscopy (STEM) imaging. The direct observation of the local barrier thickness shows a Gaussian distribution of the barrier thickness variation along the junction, from ~1 to ~2nm. We have investigated how the thickness distribution varies with oxygen pressure (Po) and oxidation time (to) and we find, in agreement with resistance measurements, that an increased to has a larger impact on barrier thickness and its uniformity compared to an increased Po.
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| 11. |
- Zeng, Lunjie, 1983, et al.
(författare)
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Nanoscale interaction layer at the interface between Al films and SiO2 substrates of Al/AlOx/Al Josephson tunnel junctions
- 2013
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:14, s. Art. no. 143905-
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Tidskriftsartikel (refereegranskat)abstract
- An interaction layer is found at the Al/SiO2 interface in Al/AlOx/Al tunnel junctions grown on SiO2 substrates. The amorphous intermixing layer has an average thickness of about 5 nm. We present the detailed structure of this interfacial layer as determined by transmission electron microscopy. The layer contains alumina with aluminum being octahedrally coordinated according to electron energy loss spectroscopy analysis rather than tetrahedrally coordinated, where the latter coordination is the most common type in amorphous alumina. Depth profiles of the Al-O and Si-O bonding characteristics were also investigated using energy loss near edge structure.
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| 12. |
- Abay, Simon, 1980, et al.
(författare)
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High Critical-Current Superconductor-InAs Nanowire-Superconductor Junctions
- 2012
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 12:11, s. 5622-5625
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication of InAs nanowires coupled to superconducting leads with high critical current and widely tunable conductance. We implemented a double lift off nanofabrication Method to get very short nanowire devices with Ohmic contacts. We observe very high critical. currents of up to 800 nA in a wire with a diameter of 80 nm. The current- voltage characteristics of longer and suspended nanowires display,either. Coulomb blockade or supercurrent depending on a local gate voltage, combining different regimes of transport in a single device.
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| 13. |
- Afzelius, M., et al.
(författare)
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Proposal for a coherent quantum memory for propagating microwave photons
- 2013
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15, s. Art. no. 065008-
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Tidskriftsartikel (refereegranskat)abstract
- We describe a multi-mode quantum memory for propagating microwave photons that combines a solid-state spin ensemble resonantly coupled to a frequency tunable single-mode microwave cavity. We first show that high efficiency mapping of the quantum state transported by a free photon to the spin ensemble is possible both for strong and weak coupling between the cavity mode and the spin ensemble. We also show that even in the weak coupling limit unit efficiency and faithful retrieval can be obtained through time reversal inhomogeneous dephasing based on spin echo techniques. This is possible provided that the cavity containing the spin ensemble and the transmission line are impedance matched. We finally discuss the prospects for an experimental implementation using a rare-earth doped crystal coupled to a superconducting resonator.
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| 14. |
- Agustí, A., et al.
(författare)
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Tripartite Genuine Non-Gaussian Entanglement in Three-Mode Spontaneous Parametric Down-Conversion
- 2020
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 125:2
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Tidskriftsartikel (refereegranskat)abstract
- We show that the states generated by a three-mode spontaneous parametric down-conversion (SPDC) interaction Hamiltonian possess tripartite entanglement of a different nature to other paradigmatic three-mode entangled states generated by the combination of two-mode SPDC interactions. While two-mode SPDC generates Gaussian states whose entanglement can be characterized by standard criteria based on two-mode quantum correlations, these criteria fail to capture the entanglement generated by three-mode SPDC. We use criteria built from three-mode correlation functions to show that the class of states recently generated in a superconducting-circuit implementation of three-mode SPDC ideally have tripartite entanglement, contrary to recent claims in the literature. These criteria are suitable for triple SPDC but we show that they fail to detect tripartite entanglement in other states which are known to possess it, which illustrates the existence of two fundamentally different notions of tripartite entanglement in three-mode continuous-variable systems.
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| 15. |
- Fan, B., et al.
(författare)
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A practical photon-number-resolving detector in the microwave regime
- 2011
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Ingår i: International Quantum Electronics Conference, IQEC 2011; Sydney;,Australia; 28 Aug -1 Sep 2011. - 9780977565771 ; , s. 2072-2074
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Konferensbidrag (refereegranskat)abstract
- We present a scheme for microwave photon detection via cross Kerr nonlinearity between two microwave modes mediated by a transmon. Using a cascaded, stochastic master equation method and conditional measurement simulations, we analyze the dependence of the probe phase shift on the control photon number. We demonstrate here that for a microwave pulse with a few photons (below 10), the relationship between the phase shift and the photon number is almost linear. Also, in our scheme, microwave photons to be detected are guided by a 1D transmission line, rather than a cavity, making it suitable for a wide range of frequencies. Finally, the signal-noise-ratio (SNR) and the feasibility of this scheme for experimental realization are discussed. Our scheme might help to build a practical photon detector in the microwave regime.
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| 16. |
- Fan, B. X., et al.
(författare)
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Breakdown of the Cross-Kerr Scheme for Photon Counting
- 2013
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 110:5
-
Tidskriftsartikel (refereegranskat)abstract
- We show, in the context of single-photon detection, that an atomic three-level model for a transmon in a transmission line does not support the predictions of the nonlinear polarizability model known as the cross-Kerr effect. We show that the induced displacement of a probe in the presence or absence of a single photon in the signal field, cannot be resolved above the quantum noise in the probe. This strongly suggests that cross-Kerr media are not suitable for photon counting or related single-photon applications. Our results are presented in the context of a transmon in a one-dimensional microwave waveguide, but the conclusions also apply to optical systems.
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| 17. |
- Hoi, Io Chun, 1984, et al.
(författare)
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Demonstration of a Single-Photon Router in the Microwave Regime
- 2011
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 107:7
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Tidskriftsartikel (refereegranskat)abstract
- We have embedded an artificial atom, a superconducting transmon qubit, in an open transmission line and investigated the strong scattering of incident microwave photons (similar to 6 GHz). When an input coherent state, with an average photon number N
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| 18. |
- Hoi, Io Chun, 1984, et al.
(författare)
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Generation of Nonclassical Microwave States Using an Artificial Atom in 1D Open Space
- 2012
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 108:26, s. art no. 263601-
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Tidskriftsartikel (refereegranskat)abstract
- We have embedded an artificial atom, a superconducting transmon qubit, in a 1D open space and investigated the scattering properties of an incident microwave coherent state. By studying the statistics of the reflected and transmitted fields, we demonstrate that the scattered states can be nonclassical. In particular, by measuring the second-order correlation function, g(2), we show photon antibunching in the reflected field and superbunching in the transmitted field. We also compare the elastically and inelastically scattered fields using both phase-sensitive and phase-insensitive measurements.
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| 19. |
- Hoi, Io Chun, 1984, et al.
(författare)
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Giant Cross–Kerr Effect for Propagating Microwaves Induced by an Artificial Atom
- 2013
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 111:5, s. article nr. 053601-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effective interaction between two microwave fields, mediated by a transmon-type superconducting artificial atom which is strongly coupled to a coplanar transmission line. The interaction between the fields and atom produces an effective cross–Kerr coupling. We demonstrate average cross–Kerr phase shifts of up to 20 degrees per photon with both coherent microwave fields at the single-photon level. Our results provide an important step toward quantum applications with propagating microwave photons.
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| 20. |
- Hoi, Io Chun, 1984, et al.
(författare)
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Microwave quantum optics with an artificial atom in one-dimensional open space
- 2013
-
Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15, s. Article Number: 025011 -
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Tidskriftsartikel (refereegranskat)abstract
- We address recent advances in microwave quantum optics with artificial atoms in one-dimensional (1D) open space. This field relies on the fact that the coupling between a superconducting artificial atom and propagating microwave photons in a 1D open transmission line can be made strong enough to observe quantum coherent effects, without using any cavity to confine the microwave photons. We investigate the scattering properties in such a system with resonant coherent microwaves. We observe the strong nonlinearity of the artificial atom and under strong driving we observe the Mollow triplet. By applying two resonant tones, we also observe the Autler-Townes splitting. Exploiting these effects, we demonstrate two quantum devices at the single-photon level in the microwave regime: the single-photon router and the photon-dnumber filter. These devices provide important steps toward the realization of an on-chip quantum network.
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| 21. |
- Hoi, Io Chun, 1984, et al.
(författare)
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Probing the quantum vacuum with an artificial atom in front of a mirror
- 2015
-
Ingår i: Nature Physics. - 1745-2481 .- 1745-2473. ; 11:12, s. 1045-1049
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Tidskriftsartikel (refereegranskat)abstract
- Quantum fluctuations of the vacuum are both a surprising and fundamental phenomenon of nature. Understood as virtual photons, they still have a very real impact, for instance, in the Casimir effects and the lifetimes of atoms. Engineering vacuum fluctuations is therefore becoming increasingly important to emerging technologies. Here, we shape vacuum fluctuations using a superconducting circuit analogue of a mirror, creating regions in space where they are suppressed. Moving an artificial atom through these regions and measuring the spontaneous emission lifetime of the atom provides us with the spectral density of the vacuum fluctuations. Using the paradigm of waveguide quantum electrodynamics, we significantly improve over previous studies of the interaction of an atom with its mirror image, observing a spectral density as low as 0.02 quanta, a factor of 50 below the mirrorless result. This demonstrates that we can hide the atom from the vacuum, even though it is exposed in free space.
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| 22. |
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| 23. |
- Johansson, J. R., et al.
(författare)
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Nonclassical microwave radiation from the dynamical Casimir effect
- 2013
-
Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 87:4, s. Art. no. 043804-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate quantum correlations in microwave radiation produced by the dynamical Casimir effect in a superconducting waveguide terminated and modulated by a superconducting quantum interference device. We apply nonclassicality tests and evaluate the entanglement for the predicted field states. For realistic circuit parameters, including thermal background noise, the results indicate that the produced radiation can be strictly nonclassical and can have a measurable amount of intermode entanglement. If measured experimentally, these nonclassicality indicators could give further evidence of the quantum nature of the dynamical Casimir radiation in these circuits.
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| 24. |
- Johansson, Robert, 1981, et al.
(författare)
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Dynamical Casimir Effect in a Superconducting Coplanar Waveguide
- 2009
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 103, s. 147003-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the dynamical Casimir effect in a coplanar waveguide (CPW) terminated by a superconducting quantum interference device (SQUID). Changing the magnetic flux through the SQUID parametrically modulates the boundary condition of the CPW, and thereby, its effective length. Effective boundary velocities comparable to the speed of light in the CPW result in broadband photon generation which is identical to the one calculated in the dynamical Casimir effect for a single oscillating mirror. We estimate the power of the radiation for realistic parameters and show that it is experimentally feasible to directly detect this nonclassical broadband radiation.
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| 25. |
- Johansson, Robert, 1981, et al.
(författare)
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Dynamical Casimir effect in superconducting microwave circuits
- 2010
-
Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 82:5, s. 052509-
-
Tidskriftsartikel (refereegranskat)abstract
- We theoretically investigate the dynamical Casimir effect (DCE) in electrical circuits based on superconducting microfabricated waveguides with tunable boundary conditions. We propose implementing a rapid modulation of the boundary conditions by tuning the applied magnetic flux through superconducting quantum-interference devices that are embedded in the waveguide circuits. We consider two circuits: (i) An open waveguide circuit that corresponds to a single mirror in free space, and (ii) a resonator coupled to a microfabricated waveguide, which corresponds to a single-sided cavity in free space. We analyze the properties of the DCE in these two setups by calculating the generated photon-flux densities, output-field correlation functions, and the quadrature squeezing spectra. We show that these properties of the output field exhibit signatures unique to the radiation due to the DCE, and could, therefore, be used for distinguishing the DCE from other types of radiation in these circuits. We also discuss the similarities and differences between the DCE, in the resonator setup, and the down-conversion of pump photons in parametric oscillators.
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| 26. |
- Krantz, Philip, 1984, et al.
(författare)
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Single-shot read-out of a superconducting qubit using a Josephson parametric oscillator
- 2016
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 7:11417
-
Tidskriftsartikel (refereegranskat)abstract
- We propose and demonstrate a read-out technique for a superconducting qubit by dispersively coupling it with a Josephson parametric oscillator. We employ a tunable quarter wavelength superconducting resonator and modulate its resonant frequency at twice its value with an amplitude surpassing the threshold for parametric instability. We map the qubit states onto two distinct states of classical parametric oscillation: one oscillating state, with 185±15 photons in the resonator, and one with zero oscillation amplitude. This high contrast obviates a following quantum-limited amplifier. We demonstrate proof-of-principle, singleshot read-out performance, and present an error budget indicating that this method can surpass the fidelity threshold required for quantum computing.
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| 27. |
- Lango Allen, Hana, et al.
(författare)
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Hundreds of variants clustered in genomic loci and biological pathways affect human height.
- 2010
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 467:7317, s. 832-8
-
Tidskriftsartikel (refereegranskat)abstract
- Most common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits, but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait. The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (P<0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways.
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| 28. |
- Laskar, Ruhina S, et al.
(författare)
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Sex specific associations in genome wide association analysis of renal cell carcinoma.
- 2019
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Ingår i: European Journal of Human Genetics. - : Springer Science and Business Media LLC. - 1018-4813 .- 1476-5438. ; 27:10, s. 1589-1598
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Tidskriftsartikel (refereegranskat)abstract
- Renal cell carcinoma (RCC) has an undisputed genetic component and a stable 2:1 male to female sex ratio in its incidence across populations, suggesting possible sexual dimorphism in its genetic susceptibility. We conducted the first sex-specific genome-wide association analysis of RCC for men (3227 cases, 4916 controls) and women (1992 cases, 3095 controls) of European ancestry from two RCC genome-wide scans and replicated the top findings using an additional series of men (2261 cases, 5852 controls) and women (1399 cases, 1575 controls) from two independent cohorts of European origin. Our study confirmed sex-specific associations for two known RCC risk loci at 14q24.2 (DPF3) and 2p21(EPAS1). We also identified two additional suggestive male-specific loci at 6q24.3 (SAMD5, male odds ratio (ORmale) = 0.83 [95% CI = 0.78-0.89], Pmale = 1.71 × 10-8 compared with female odds ratio (ORfemale) = 0.98 [95% CI = 0.90-1.07], Pfemale = 0.68) and 12q23.3 (intergenic, ORmale = 0.75 [95% CI = 0.68-0.83], Pmale = 1.59 × 10-8 compared with ORfemale = 0.93 [95% CI = 0.82-1.06], Pfemale = 0.21) that attained genome-wide significance in the joint meta-analysis. Herein, we provide evidence of sex-specific associations in RCC genetic susceptibility and advocate the necessity of larger genetic and genomic studies to unravel the endogenous causes of sex bias in sexually dimorphic traits and diseases like RCC.
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| 29. |
- Peropadre, Borja, et al.
(författare)
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Approaching perfect microwave photodetection in circuit QED
- 2011
-
Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 84
-
Tidskriftsartikel (refereegranskat)abstract
- In order to apply all ideas from quantum optics to the field of quantum circuits, one of the missing ingredients is a high-efficiency single-photon detector. In this work we propose a design for such a device which successfully reaches 100% efficiency with only one absorber. Our photon detector consists of a three-level system (a phase qubit) coupled to a semi-infinite one-dimensional waveguide (a microwave transmission line) which performs highly efficient photodetection in a simplified manner as compared to previous proposals. Using the tools of quantum optics we extensively study the scattering properties of realistic wave packets against this device, thereby computing the efficiency of the detector. We find that the detector has many operating modes, can detect detuned photons, is robust against design imperfections, and can be made broadband by using more than one absorbing element in the design. Many of these ideas could be translated to other single-mode photonic or plasmonic waveguides interacting with three-level atoms or quantum dots.
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| 30. |
- Peropadre, B., et al.
(författare)
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Scattering of coherent states on a single artificial atom
- 2013
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15, s. Article Number: 035009-
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we theoretically analyze a circuit quantum electrodynamics design where propagating quantum microwaves interact with a single artificial atom, a single Cooper-pair box. In particular, we derive a master equation in the so-called transmon regime, including coherent drives. Inspired by recent experiments, we then apply the master equation to describe the dynamics in both a two-level and a three-level approximation of the atom. In the two-level case, we also discuss how to measure photon antibunching in the reflected field and how it is affected by finite temperature and finite detection bandwidth.
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| 31. |
- Persson, Fredrik, 1978, et al.
(författare)
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Excess Dissipation in a Single-Electron Box: The Sisyphus Resistance
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:3, s. 953-957
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the ac response of a single-electron box (SEB). We apply a radio frequency signal with a Frequency larger than the tunneling rate and drive the system out of equilibrium. We observe much more dissipation in the SEB then one would expect from a simple circuit model, We can explain this in terms of a mechanism that we call the Sisyphus resistance. The Sisyphus resistance has a strong gate dependence which can be used for electrometery applications.
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| 32. |
- Persson, Fredrik, 1978, et al.
(författare)
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Fast readout of a single Cooper-pair box using its quantum capacitance
- 2010
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 82:13, s. Article Number: 134533 -
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated a single Cooper-pair box (SCB) together with an on-chip lumped element resonator. By utilizing the quantum capacitance of the SCB, its state can be read out by detecting the phase of a radio-frequency signal reflected off the resonator. The resonator was optimized for fast readout. By studying quasiparticle tunneling events in the SCB, we have characterized the performance of the readout and found that we can perform a single-shot parity measurement, with a signal-to-noise ratio of 1, in approximately 50 ns. This is an order of magnitude faster than previously reported measurements.
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| 33. |
- Peternell, Mark, 1974, et al.
(författare)
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A new approach to crystallographic orientation measurement for apatite fission track analysis: Effects of crystal morphology and implications for automation
- 2009
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541. ; 265, s. 527-539
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Tidskriftsartikel (refereegranskat)abstract
- Apatite fission track analysis and in particular, computer-assisted fission track recognition require the determination of crystallographic orientation, crystal morphology, cracks, fractures and inclusions. The selection of a crystal for fission track analysis has largely been based on its surface and track etching characteristics that, in conventional fission track dating, is performed by the analyst. This requires manual scanning of the entire mount for suitable grains, which is a very time-intensive process during manual fission track counting. Therefore, a computer-assisted grain characterisation system is of interest to allow for an automated pre-selection of suitable crystals. With the use of a fully automated Fabric Analyser, c-axis orientations can be measured inside an apatite crystal for each pixel with a spatial resolution of 5 μm. The results are represented in geometric quality and retardation maps consisting of the c-axis orientations for each pixel and two quality values evaluating each orientation. These maps allow the determination of the crystallography of the apatite grain as well as its outline. In addition, most of the crystal morphologies, fractures and impurities, which can influence automated fission track recognition techniques based on image analysis, are determinable using the quality maps. On the other hand, the method is not sensitive to smaller crystal cracks, high fission track densities or coating. The quantification of the crystal geometric properties by this method is a step forward to develop a fully automated fission track analysis process. © 2009 Elsevier B.V. All rights reserved.
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| 34. |
- Peternell, Mark, 1974, et al.
(författare)
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Evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using EBSD and fabric analyser techniques
- 2010
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Ingår i: Journal of Structural Geology. - : Elsevier BV. - 0191-8141 .- 1873-1201. ; 32:6, s. 803-817
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Tidskriftsartikel (refereegranskat)abstract
- Quartz crystallographic preferred orientations (CPO) from three distinct orthogneisses using both the Electron Back Scatter Diffraction (EBSD) and Fabric Analyser (FA) techniques reveal a clear trend from basal < a > and rhomb < a + c > slip for high P-T conditions (670 +/- 20 degrees C/9 kbar), rhomb < a + c > and basal < a > slip for medium P-T (590 +/- 15 degrees C/6 kbar) and a dominance of prism < a > slip for lower P T conditions (<570 degrees C/4-5 kbar). The textural variations are interpreted in terms of a temperature field gradient and microscale strain partitioning controlled by a weak feldspar matrix that can locally invert the expected slip system sequences. Locally quartz CPUs are different within one thin section, and in comparison to bulk orientation measurements both, EBSD and the Fabric Analyser techniques are ideal to determine such textural heterogeneities. While the EBSD is a powerful technique to determine the full CPO, measurements from similar locations inside several quartz grains from the orthogneisses and an annealed and undeformed quartzite show that the FA is an accurate tool to determine CPUs of c-axis orientations in uniaxial materials. In a CPO focussed study the FA is a cheap alternative to EBSD as the analysis of whole thin section can be accomplished in a very short time, with minimal sample preparation. With the FA it is possible to evaluate the CPUs of several samples quickly with an accuracy that allows identification of the main slip systems and their homogeneity.
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| 35. |
- Przybyszewski, A. W., et al.
(författare)
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Basic difference between brain and computer: Integration of asynchronous processes implemented as hardware model of the retina
- 2007
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Ingår i: IEEE Transactions on Neural Networks. - : Institute of Electrical and Electronics Engineers (IEEE). - 1045-9227. ; 18:1, s. 70-85
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Tidskriftsartikel (refereegranskat)abstract
- There exists a common view that the brain acts like a Turing machine: The machine reads information from an infinite tape (sensory data) and, on the basis of the machine's state and information from the tape, an action (decision) is made. The main problem with this model lies in how to synchronize a large number of tapes in an adaptive way so that the machine is able to accomplish tasks such as object classification. We propose that such mechanisms exist already in the eye. A popular view is that the retina, typically associated with high gain and adaptation for light processing, is actually performing local preprocessing by means of its center-surround receptive field. We would like to show another property of the retina: The ability to integrate many independent processes. We believe that this integration is implemented by synchronization of neuronal oscillations. In this paper, we present a model of the retina consisting of a series of coupled oscillators which can synchronize on several scales. Synchronization is an analog process which is converted into a digital spike train in the output of the retina. We have developed a hardware implementation of this model, which enables us to carry out rapid simulation of multineuron oscillatory dynamics. We show that the properties of the spike trains in our model are similar to those found in vivo in the cat retina.
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| 36. |
- Sandberg, Martin, 1977, et al.
(författare)
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Exploring circuit quantum electrodynamics using a widely tunable superconducting resonator
- 2009
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Ingår i: Physica Scripta. - 1402-4896 .- 0031-8949. ; T137, s. Art. no. 014018-
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated and characterized systems consisting of superconducting quantum bits (qubits) of the transmon type, coupled to a tunable transmission line resonator. The resonator consists of a superconducting quarter wavelength coplanar waveguide (CPW) resonator that is made tunable by terminating the transmission line to ground through a superconducting quantum interference device (SQUID). Here we present measurements on two devices where we observe Rabi oscillations as we drive the qubit, and vacuum Rabi splitting both as we tune the qubits into resonance with the resonator and as we tune the resonator into resonance with the qubits. We also observe coherent interaction between two resonant qubits. In addition, we demonstrate that we can calculate the response very accurately using a multilevel Hamiltonian.
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| 37. |
- Sandberg, Martin, 1977, et al.
(författare)
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Fast tuning of superconducting microwave cavities
- 2008
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Ingår i: Proc. 2nd International Workshop on Solid-State Quantum Computing. - 9780735406056 ; , s. 12-21
-
Konferensbidrag (refereegranskat)abstract
- Photons are fundamental excitations of electromagnetic fields and can be captured in cavities. For a given cavity with a certain size, the fundamental mode has a fixed frequency f which gives the photons a specific "color". The cavity also has a typical lifetime tau, which results in a finite linewidth delta f. If the size of the cavity is changed fast compared to tau, and so that the frequency change Delta f >> delta f, then it is possible to change the "color" of the captured photons. Here we demonstrate superconducting microwave cavities, with tunable effective lengths. The tuning is obtained by varying a Josephson inductance at one end of the cavity. We show data on four different samples and demonstrate tuning by several hundred linewidths in a time Delta t
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| 38. |
- Sandberg, Martin, 1977, et al.
(författare)
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Tuning the field in a microwave resonator faster than the photon lifetime
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:20, s. 203501-
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated and characterized tunable superconducting transmission line resonators. To change the resonance frequency, we modify the boundary condition at one end of the resonator through the tunable Josephson inductance of a superconducting quantum interference device. We demonstrate a large tuning range (several hundred megahertz), high quality factors (10(4)), and that we can change the frequency of a few-photon field on a time scale orders of magnitude faster than the photon lifetime of the resonator. This demonstration has implications in a variety of applications.
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| 39. |
- Sathyamoorthy, Sankar Raman, 1984, et al.
(författare)
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Quantum Nondemolition Detection of a Propagating Microwave Photon
- 2014
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 112:9, s. art. no. 093601-
-
Tidskriftsartikel (refereegranskat)abstract
- The ability to nondestructively detect the presence of a single, traveling photon has been a long-standing goal in optics, with applications in quantum information and measurement. Realizing such a detector is complicated by the fact that photon-photon interactions are typically very weak. At microwave frequencies, very strong effective photon-photon interactions in a waveguide have recently been demonstrated. Here we show how this type of interaction can be used to realize a quantum nondemolition measurement of a single propagating microwave photon. The scheme we propose uses a chain of solid-state three-level systems (transmons) cascaded through circulators which suppress photon backscattering. Our theoretical analysis shows that microwave-photon detection with fidelity around 90% can be realized with existing technologies.
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| 40. |
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| 41. |
- Schuermans, Steven, et al.
(författare)
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An On-Chip Mach-Zehnder Interferometer in the Microwave Regime
- 2011
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 21:3, s. 448-451
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Tidskriftsartikel (refereegranskat)abstract
- The design, simulation and measurements of an on-chip Mach-Zehnder interferometer operating in the microwave regime are described. Using microwave signals in microfabricated superconducting Al waveguides, the concept of an interferometer is transferred from optics to on-chip. Tuning of the path length of one of the interferometer arms is executed through the tunable inductance of a SQUID. By placing one or more SQUIDs in the waveguide structure and by varying the magnetic flux through the SQUID loop, the total SQUID inductance can be tuned. In this way, a phase difference leading to destructive or constructive interference at the interferometer output can be achieved. Thorough software simulations were performed to determine the different design parameters, assign a desired working frequency and provide a reference for comparison with experimental results. Measurements at 300 mK show an effective working frequency close to the simulations, with a deviation smaller than 0.05 GHz. The behavior of the interferometer is very similar to the simulations as well. The on-off ratio exceeds 40 dB.
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| 42. |
- Simoen, Michael Roger Andre, 1986, et al.
(författare)
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Characterization of a multimode coplanar waveguide parametric amplifier
- 2015
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 118:15, s. 154501-
-
Tidskriftsartikel (refereegranskat)abstract
- We characterize a Josephson parametric amplifier based on a flux-tunable quarter-wavelength resonator. The fundamental resonance frequency is ∼1 GHz, but we use higher modes of the resonator for our measurements. An on-chip tuning line allows for magnetic flux pumping of the amplifier. We investigate and compare degenerate parametric amplification, involving a single mode, and nondegenerate parametric amplification, using a pair of modes. We show that we reach quantum-limited noise performance in both cases.
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| 43. |
- Staudt, Matthias, 1977, et al.
(författare)
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Coupling of an erbium spin ensemble to a superconducting resonator
- 2012
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 1361-6455 .- 0953-4075. ; 45:12, s. Art. no. 124019-
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Tidskriftsartikel (refereegranskat)abstract
- A quantum coherent interface between optical and microwave photons can be used as a basic building block within a future quantum information network. The interface is envisioned as an ensemble of rare-earth ions coupled to a superconducting resonator, allowing for coherent transfer between optical and microwave photons. Towards this end, we have realized a hybrid device coupling a Er3+-doped Y2SiO5 crystal in a superconducting coplanar waveguide cavity. We observe a collective spin coupling of 4 MHz and a spin linewidth of down to 75 MHz.
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| 44. |
- Sundqvist, Kyle, 1978, et al.
(författare)
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The pumpistor: A linearized model of a flux-pumped superconducting quantum interference device for use as a negative-resistance parametric amplifier
- 2013
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:102603
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Tidskriftsartikel (refereegranskat)abstract
- We describe a circuit model for a flux-driven Superconducting QUantum Interference Device (SQUID). This is useful for developing insight into how these devices perform as active elements in parametric amplifiers. The key concept is that frequency mixing in a flux-pumped SQUID allows for the appearance of an effective negative resistance. In the three-wave, degenerate case treated here, a negative resistance appears only over a certain range of allowed input signal phase. This model readily lends itself to testable predictions of more complicated circuits.
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| 45. |
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| 46. |
- Wilson, Christopher, 1974, et al.
(författare)
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Dressed relaxation and dephasing in a strongly driven two-level system
- 2010
-
Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 81:2, s. Art. no. 024520-
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Tidskriftsartikel (refereegranskat)abstract
- We study relaxation and dephasing in a strongly driven two-level system interacting with its environment. We develop a theory which gives a straightforward physical picture of the complex dynamics of the system in terms of dressed states. In addition to the dressing of the energy diagram, we describe the dressing of relaxation and dephasing. We find a good quantitative agreement between the theoretical calculations and measurements of a superconducting qubit driven by an intense microwave field. The competition of various processes leads to a rich structure in the observed behavior, including signatures of population inversion.
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| 47. |
- Wilson, Christopher J.L., et al.
(författare)
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Deformation of polycrystalline D2O ice: Its sensitivity to temperature and strain-rate as an analogue for terrestrial ice
- 2020
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X. ; 532
-
Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline deuterated ice (D2O) was deformed over a range of high-temperatures (−20 to −1 °C; 0.92–0.99Tm) during in situ neutron diffraction texture and grain-size analysis. This allowed for a continuous monitoring of the evolution of rheology, texture, grain-numbers and the type of microstructures, which are compared to those encountered in basal sections of ice-sheets. We quantify the textural evolution with J-index changes as a function of strain-rate and temperature. Three sets of unconfined samples were deformed at displacement rates of 1×10−5 s−1 (fast) 2.5×10−6 s−1 (medium) and 6×10−7 s−1 (slow). Dislocation creep is proposed as the main deformation mechanism with sub-grain rotation more significant at lower temperatures (0.92Tm) and/or higher strain-rates. At higher-temperatures (0.99Tm) and/or lower strain-rates dynamic recrystallization is dominated by grain boundary migration, typified by grains with highly curved or lobate grain boundaries, and leading to rheological softening of the ice. From initially randomly oriented [c]-axes, a texture comprising 30–35° cones parallel to the compression axis develops, which is comparable to textures observed in the upper levels of polar ice-sheets. There is also a strain-rate dependence on the development of normalized [c]-axis intensities, which is in competition with strain magnitude and temperature. At lower temperatures (≤10 °C), small increments of strain or slower strain-rates, the cone-angle and textural strength decrease with a dominant textural component parallel to the compression axis. This may be an explanation for the vertical [c]-axis concentrations observed in polar ice cores.
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| 48. |
- Wilson, Christopher J L, et al.
(författare)
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Evaluating ice fabrics using fabric analyser techniques in Sørsdal Glacier, East Antarctica
- 2011
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 57, s. 881-894
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Tidskriftsartikel (refereegranskat)abstract
- Ice cores (∼4 m long) obtained from areas of different surface velocities near the terminus of Sørsdal Glacier, East Antarctica, have been investigated using two versions of a fabric analyser (G50). In sections parallel to the flow plane, the microstructure is typically interlocking with elongate grains that parallel air-bubble elongation, X, reflecting their development in an earlier ductile regime. The c-axis fabric patterns vary with respect to X and vary from single-double maxima to asymmetric smallcircle girdles oblique to the planar foliation, which can be attributed to a simple shear regime. The siteto-site variations in the c-axis patterns can be related to areas of different surface velocities, the asymmetry of fabrics correlating with localized strain variations and differences in the deformation path, but not to the current strain pattern recorded by the near-surface deformation conditions. Overprinting fractures have little effect on microstructure except for local dissolution and precipitation along stylolitic surfaces. Comparison of results from the two different fabric analysers reveals that with a higher pixel resolution the incorporation of additional monochromatic light-emitting diodes and repositioning of a retarder plate produce more reliable c-axis measurements.
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| 49. |
- Wilson, Christopher J L, et al.
(författare)
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Ice deformed in compression and simple shear: Control of temperature and initial fabric
- 2012
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Ingår i: Journal of Glaciology. - 0022-1430. ; 58, s. 11-22
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Tidskriftsartikel (refereegranskat)abstract
- Layered and polycrystalline ice was experimentally deformed in general shear involving axial compression (strain magnitude 0.5-17%) and simple shear (strain magnitude λ = 0.1-1.4). As the temperature is increased from -20°C to -2°C, there is at least a twofold enhancement in octahedral shear strain rate, which coincides with the onset of extensive dynamic recrystallization and a change in grain-size distribution at -15°C. Between -15°C and -10°C the c-axis preferred orientation rapidly evolves with the initiation of two-maxima fabrics in shear zones. From -10°C to -2°C there is progressive evolution of a final c-axis pattern that is asymmetric with respect to the direction of shortening, with a strong maximum at ̃5° to the pole of the shear zone, a sense of asymmetry in the direction of the shear, and a secondary maximum inclined at ̃45° to the plane of shearing. An initial c-axis preferred orientation plays a critical role in the initial mechanical evolution. In contrast to established ideas, a strong alignment of basal planes parallel to the plane of easy glide inhibited deformation and there was an increased component of strain hardening until recrystallization processes become dominant.
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| 50. |
- Wilson, Christopher J.L., et al.
(författare)
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Partial melting in polycrystalline ice: pathways identified in 3D neutron tomographic images
- 2024
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Ingår i: Cryosphere. - 1994-0416 .- 1994-0424. ; 18:2, s. 819-836
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Tidskriftsartikel (refereegranskat)abstract
- In frozen cylinders composed of deuterium ice (Tm+3.8C) and 10% water ice (Tm0C), it is possible to track melt pathways produced by increasing the temperature during deformation. Raising the temperature to +2C produces water (H2O) which combines with the D2O ice to form mixtures of HDO. As a consequence of deformation, HDO and H2O meltwater are expelled along conjugate shear bands and as compactional melt segregations. Melt segregations are also associated with high-porosity networks related to the location of transient reaction fronts where the passage of melt-enriched fluids is controlled by the localized ductile yielding and lowering of the effective viscosity. Accompanying the softening, the meltwater also changes and weakens the crystallographic fabric development of the ice. Our observations suggest meltwater-enriched compaction and shear band initiation provide instabilities and the driving force for an enhancement of permeability in terrestrial ice sheets and glaciers.
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