| 1. |
- Abuhattum, Shada, et al.
(författare)
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Intracellular Mass Density Increase Is Accompanying but Not Sufficient for Stiffening and Growth Arrest of Yeast Cells
- 2018
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 6:NOV
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Tidskriftsartikel (refereegranskat)abstract
- Many organisms, including yeast cells, bacteria, nematodes, and tardigrades, endure harsh environmental conditions, such as nutrient scarcity, or lack of water and energy for a remarkably long time. The rescue programs that these organisms launch upon encountering these adverse conditions include reprogramming their metabolism in order to enter a quiescent or dormant state in a controlled fashion. Reprogramming coincides with changes in the macromolecular architecture and changes in the physical and mechanical properties of the cells. However, the cellular mechanisms underlying the physical-mechanical changes remain enigmatic. Here, we induce metabolic arrest of yeast cells by lowering their intracellular pH. We then determine the differences in the intracellular mass density and stiffness of active and metabolically arrested cells using optical diffraction tomography (ODT) and atomic force microscopy (AFM). We show that an increased intracellular mass density is associated with an increase in stiffness when the growth of yeast is arrested. However, increasing the intracellular mass density alone is not sufficient for maintenance of the growth-arrested state in yeast cells. Our data suggest that the cytoplasm of metabolically arrested yeast displays characteristics of a solid. Our findings constitute a bridge between the mechanical behavior of the cytoplasm and the physical and chemical mechanisms of metabolically arrested cells with the ultimate aim of understanding dormant organisms.
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| 2. |
- Afzali, Maryam, et al.
(författare)
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Quantification of Tissue Microstructure Using Tensor-Valued Diffusion Encoding: Brain and Body
- 2022
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 10
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Forskningsöversikt (refereegranskat)abstract
- Diffusion-weighted magnetic resonance imaging (DW-MRI) is a non-invasive technique to probe tissue microstructure. Conventional Stejskal–Tanner diffusion encoding (i.e., encoding along a single axis), is unable to disentangle different microstructural features within a voxel; If a voxel contains microcompartments that vary in more than one attribute (e.g., size, shape, orientation), it can be difficult to quantify one of those attributes in isolation using Stejskal–Tanner diffusion encoding. Multidimensional diffusion encoding, in which the water diffusion is encoded along multiple directions in q-space (characterized by the so-called “b-tensor”) has been proposed previously to solve this problem. The shape of the b-tensor can be used as an additional encoding dimension and provides sensitivity to microscopic anisotropy. This has been applied in multiple organs, including brain, heart, breast, kidney and prostate. In this work, we discuss the advantages of using b-tensor encoding in different organs.
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| 3. |
- Ahmadi, Delaram, et al.
(författare)
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Nanoscale Structure and Dynamics of Model Membrane Lipid Raft Systems, Studied by Neutron Scattering Methods
- 2022
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Quasi-elastic neutron scattering (QENS) and small angle neutron scattering (SANS), in combination with isotopic contrast variation, have been used to determine the structure and dynamics of three-component lipid membranes, in the form of vesicles, comprising an unsaturated [palmitoyl-oleoyl-phosphatidylcholine (POPC) or dioleoyl-phosphatidylcholine (DOPC)], a saturated phospholipid (dipalmitoyl-phosphatidylcholine (DPPC)), and cholesterol, as a function temperature and composition. SANS studies showed vesicle membranes composed of a 1:1:1 molar ratio of DPPC:DOPC:cholesterol and a 2:2:1 molar ratio of DPPC:POPC:cholesterol phase separated, forming lipid rafts of ∼18 and ∼7 nm diameter respectively, when decreasing temperature from 308 to 297 K. Phase separation was reversible upon increasing temperature. The larger rafts observed in systems containing DOPC are attributed to the greater mis-match in lipid alkyl chains between DOPC and DPPC, than for POPC and DPPC. QENS studies, over the temperature range 283–323K, showed that the resulting data were best modelled by two Lorentzian functions: a narrow component, describing the “in-plane” lipid diffusion, and a broader component, describing the lipid alkyl chain segmental relaxation. The overall “in-plane” diffusion was found to show a significant reduction upon increasing temperature due to the vesicle membranes transitioning from one containing rafts to one where the component lipids are homogeneously mixed. The use of different isotopic combinations allowed the measured overall reduction of in-plane diffusion to be understood in terms of an increase in diffusion of the saturated DPPC lipid and a corresponding decrease in diffusion of the unsaturated DOPC/POPC lipid. As the rafts are considered to be composed principally of saturated lipid and cholesterol, the breakdown of rafts decreases the exposure of the DPPC to cholesterol whilst increasing the exposure of cholesterol to unsaturated lipid. These results show the sensitivity of lipid diffusion to local cholesterol concentration, and the importance of considering the local, rather that the global composition of a membrane when understanding the diffusion processes of lipids within the membrane. The novel combination of SANS and QENS allows a non-intrusive approach to characterize the structure and dynamics occurring in phase-separated model membranes which are designed to mimic the lateral heterogeneity of lipids seen in cellular membranes–a heterogeneity that can have pathological consequences.
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| 4. |
- Becker, K. S., et al.
(författare)
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Ab initio symmetry-adapted emulator for studying emergent collectivity and clustering in nuclei
- 2023
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- We discuss emulators from the ab initio symmetry-adapted no-core shell-model framework for studying the formation of alpha clustering and collective properties without effective charges. We present a new type of an emulator, one that utilizes the eigenvector continuation technique but is based on the use of symplectic symmetry considerations. This is achieved by using physically relevant degrees of freedom, namely, the symmetry-adapted basis, which exploits the almost perfect symplectic symmetry in nuclei. Specifically, we study excitation energies, point-proton root-mean-square radii, along with electric quadrupole moments and transitions for 6Li and 12C. We show that the set of parameterizations of the chiral potential used to train the emulators has no significant effect on predictions of dominant nuclear features, such as shape and the associated symplectic symmetry, along with cluster formation, but slightly varies details that affect collective quadrupole moments, asymptotic normalization coefficients, and alpha partial widths up to a factor of two. This makes these types of emulators important for further constraining the nuclear force for high-precision nuclear structure and reaction observables.
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| 5. |
- Boito, Deneb, et al.
(författare)
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Multidimensional Diffusion MRI Methods With Confined Subdomains
- 2022
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion Magnetic Resonance Imaging (dMRI) is an imaging technique with exquisite sensitivity to the microstructural properties of heterogeneous media. The conventionally adopted acquisition schemes involving single pulsed field gradients encode the random motion of water molecules into the NMR signal, however typically conflating the effects of different sources contributing to the water motion. Time-varying magnetic field gradients have recently been considered for disentangling such effects during the data encoding phase, opening to the possibility of adding specificity to the recovered information about the mediums microstructure. Such data is typically represented via a diffusion tensor distribution (DTD) model, thus assuming the existence of several non-exchanging compartments in each of which diffusion is unrestricted. In this work, we consider a model that takes confinement into account and possesses a diffusion time-dependence closer to that of restricted diffusion, to replace the free diffusion assumption in multidimensional diffusion MRI methods. We first demonstrate how the confinement tensor model captures the relevant signal modulations impressed by water diffusing in both free and closed spaces, for data simulated with a clinically feasible protocol involving time-varying magnetic field gradients. Then, we provide the basis for incorporating this model into two multidimensional dMRI methods, and attempt to recover a confinement tensor distribution (CTD) on a human brain dataset.
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| 6. |
- Brenner, Richard, et al.
(författare)
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Multi Gigabit Wireless Data Transfer in Detectors at Future Colliders
- 2022
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Ingår i: Frontiers in Physics. - : Frontiers Media S.A.. - 2296-424X. ; 10
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Forskningsöversikt (refereegranskat)abstract
- The WADAPT (Wireless Allowing Data And Power Transmission) consortium has been formed to identify the specific needs of different projects that might benefit from wireless communication technologies with the objective of providing a common platform for research and development in order to optimize effectiveness and cost. Wireless technologies have developed extremely fast over the last decade and are now mature enough to be a promising alternative to cables and optical links, with a possibility of revolutionizing detector design. Although wireless readout has the qualities and properties to be used in many collider detectors, this article focuses on the transmission of large amount of data from vertex detectors at high rate, low power budget and in potential high radiation environment. For vertex detectors, the 60 GHz band has proven to be adequate and commercial products are already available, providing 6 Gbps data links. This technology allows efficient partitioning of detectors in topological regions of interest, with the possibility of adding intelligence on the detector to perform four-dimensional reconstruction of the tracks and vertices online, in order to attach the tracks to their vertex with great efficiency even in difficult experimental conditions, and conveniently substitutes a mass of materials (cables and connectors). Early transceiver module products have been successfully tested for signal confinement, crosstalk, electromagnetic immunity and resistance to radiation. In the long run, emerging 140 GHz bands could also be used for higher data rates (>100 Gbps) at future high energy and luminosity hadron colliders.
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| 7. |
- Brzozowska, Beata, et al.
(författare)
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Monte Carlo Modeling of DNA Lesions and Chromosomal Aberrations Induced by Mixed Beams of Alpha Particles and X-Rays
- 2020
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Prediction of health risks associated with exposure to mixed beams of high- and low-linear energy transfer ionizing radiation is based on the assumption that the biological effect caused by mixed radiation equals the sum of effects resulting from the action of individual beam components. Experimental studies have demonstrated that the cellular effects in cells exposed to mixed radiations are higher than that calculated based on the assumption of additivity. The present work contains a comparative analysis of published results on chromosomal aberrations in human peripheral blood lymphocytes exposed to mixed beams of alpha particles and X-rays with computer simulations using the PARTRAC program based on Monte Carlo methods. PARTRAC was used to calculate the levels of DNA single-strand breaks (SSB) and double-strand breaks (DSB—both complex and simple) and the level of chromosomal aberrations. SSB and DSB yields were found to be additive. A synergistic effect was obtained at the level of chromosomal aberrations, being in good agreement with the experimental results. This result demonstrates that the synergistic action of mixed beams results from processing of SSB and DSB and not from their initial frequencies. The level of synergy was dependent on the composition of the mixed beam, with highest level at 50:50 ratio of alpha particles and X-rays.
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| 8. |
- Cacciapaglia, Giacomo, et al.
(författare)
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Light scalars in composite Higgs models
- 2019
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Ingår i: Frontiers of Physics. - : Frontiers Media SA. - 2296-424X. ; 7:12
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Tidskriftsartikel (refereegranskat)abstract
- A composite Higgs boson is likely to be accompanied by additional light states generated by the same dynamics. This expectation is substantiated when realising the composite Higgs mechanism by an underlying gauge theory. We review the dynamics of such objects, which may well be the first sign of compositeness at colliders. We also update our previous analysis of the bounds from LHC searches to the latest results, and discuss the projected reach of the High-Luminosity run.
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| 9. |
- Cardoso, Fernando R., et al.
(författare)
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Detailed Account of Complexity for Implementation of Circuit-Based Quantum Algorithms
- 2021
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- In this review article, we are interested in the detailed analysis of complexity aspects of both time and space that arises from the implementation of a quantum algorithm on a quantum based hardware. In particular, some steps of the implementation, as the preparation of an arbitrary superposition state and readout of the final state, in most of the cases can surpass the complexity aspects of the algorithm itself. We present the complexity involved in the full implementation of circuit-based quantum algorithms, from state preparation to the number of measurements needed to obtain good statistics from the final states of the quantum system, in order to assess the overall space and time costs of the processes.
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| 10. |
- Chintada, Bhaskara R., et al.
(författare)
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Phase-Aberration Correction in Shear-Wave Elastography Imaging Using Local Speed-of-Sound Adaptive Beamforming
- 2021
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Ingår i: Frontiers in Physics. - : Frontiers Media S.A.. - 2296-424X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Shear wave elasticity imaging (SWEI) is a non-invasive imaging modality that provides tissue elasticity information by measuring the travelling speed of an induced shear-wave. It is commercially available on clinical ultrasound scanners and popularly used in the diagnosis and staging of liver disease and breast cancer. In conventional SWEI methods, a sequence of acoustic radiation force (ARF) pushes are used for inducing a shear-wave, which is tracked using high frame-rate multi-angle plane wave imaging (MA-PWI) to estimate the shear-wave speed (SWS). Conventionally, these plane waves are beamformed using a constant speed-of-sound (SoS), assuming an a-priori known and homogeneous tissue medium. However, soft tissues are inhomogeneous, with intrinsic SoS variations. In this work, we study the SoS effects and inhomogeneities on SWS estimation, using simulation and phantoms experiments with porcine muscle as an abbarator, and show how these aberrations can be corrected using local speed-of-sound adaptive beamforming. For shear-wave tracking, we compare standard beamform with spatially constant SoS values to software beamforming with locally varying SoS maps. We show that, given SoS aberrations, traditional beamforming using a constant SoS, regardless of the utilized SoS value, introduces a substantial bias in the resulting SWS estimations. Average SWS estimation disparity for the same material was observed over 4.3 times worse when a constant SoS value is used compared to that when a known SoS map is used for beamforming. Such biases are shown to be corrected by using a local SoS map in beamforming, indicating the importance of and the need for local SoS reconstruction techniques.
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