| 431. |
- Bianchi, M., et al.
(författare)
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One-dimensional spin texture of Bi(441): Quantum spin Hall properties without a topological insulator
- 2015
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 91:16
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Tidskriftsartikel (refereegranskat)abstract
- The high index (441) surface of bismuth has been studied using scanning tunneling microscopy (STM), angle resolved photoemission spectroscopy (APRES), and spin-resolved ARPES. The surface is strongly corrugated, exposing a regular array of (110)-like terraces. Two surface localized states are observed, both of which are linearly dispersing in one in-plane direction (k(x)), and dispersionless in the orthogonal in-plane direction (k(y)), and both of which have a Dirac-like crossing at k(x) = 0. Spin ARPES reveals a strong in-plane polarization, consistent with Rashba-like spin-orbit coupling. One state has a strong out-of-plane spin component, which matches with the miscut angle, suggesting its possible origin as an edge state. The electronic structure of Bi(441) has significant similarities with topological insulator surface states and is expected to support one-dimensional quantum spin Hall-like coupled spin-charge transport properties with inhibited backscattering, without requiring a topological insulator bulk.
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| 432. |
- Biswas, Deepnarayan, et al.
(författare)
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Ultrafast Triggering of Insulator-Metal Transition in Two-Dimensional VSe2
- 2021
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 21:5, s. 1968-1975
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Tidskriftsartikel (refereegranskat)abstract
- The transition-metal dichalcogenide VSe2 exhibits an increased charge density wave transition temperature and an emerging insulating phase when thinned to a single layer. Here, we investigate the interplay of electronic and lattice degrees of freedom that underpin these phases in single-layer VSe2 using ultrafast pump-probe photoemission spectroscopy. In the insulating state, we observe a light-induced closure of the energy gap, which we disentangle from the ensuing hot carrier dynamics by fitting a model spectral function to the time-dependent photoemission intensity. This procedure leads to an estimated time scale of 480 fs for the closure of the gap, which suggests that the phase transition in single-layer VSe2 is driven by electron-lattice interactions rather than by Mott-like electronic effects. The ultrafast optical switching of these interactions in SL VSe2 demonstrates the potential for controlling phase transitions in 2D materials with light.
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| 433. |
- Bollmark, Gunnar, et al.
(författare)
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Solving 2D and 3D lattice models of correlated fermions : combining matrix product states with mean-field theory
- 2023
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Ingår i: Physical Review X. - : American Physical Society. - 2160-3308. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Correlated electron states are at the root of many important phenomena including unconventional superconductivity (USC), where electron pairing arises from repulsive interactions. Computing the properties of correlated electrons, such as the critical temperature Tc for the onset of USC, efficiently and reliably from the microscopic physics with quantitative methods remains a major challenge for almost all models and materials. In this theoretical work, we combine matrix product states (MPS) with static mean field (MF) to provide a solution to this challenge for quasi-one-dimensional (Q1D) systems: two- and three-dimensional materials comprised of weakly coupled correlated 1D fermions. This MPS+MF framework for the ground state and thermal equilibrium properties of Q1D fermions is developed and validated for attractive Hubbard systems first, and further enhanced via analytical field theory. We then deploy it to compute Tc for superconductivity in 3D arrays of weakly coupled, doped, and repulsive Hubbard ladders. The MPS+MF framework thus enables the quantitative study of USC and high-Tc superconductivity—and potentially many more correlated phases—in fermionic Q1D systems based directly on their microscopic parameters, in ways inaccessible to previous methods. This approach further allows one to treat competing macroscopic orders, such as superconducting and insulating ones, on an equal footing. Benchmarks of the framework using auxiliary-field quantum Monte Carlo techniques show that the overestimation of, e.g., Tc due to its mean-field component, is near constant in microscopic parameters. These features of the MPS+MF approach to correlated fermions open up the possibility of designing deliberately optimized Q1D superconductors, from experiments in ultracold gases to synthesizing new materials.
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| 434. |
- Carlbring, Per, et al.
(författare)
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Internet-Delivered Attention Training for SAD : who Responds and Why
- 2014
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Ingår i: Abstracts from the 48th Annual Convention of the Association for Behavioral and Cognitive Therapies.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- While attention modification programs (AMP) have shown promise as laboratory-based treatments for social anxiety disorder, trials of internet-delivered AMP have not yielded significant differences between active and control conditions. To address these inconsistencies, we examined the moderational and mediational role of attention bias in the efficacy of attention training. We compared data reported by Carlbring et al. (2012) to an identical AMP condition, with the exception that participants were instructed to activate social anxiety fears prior to each attention training session (AMP+FACT; n=39). We also compared all attention training groups to an internet-delivered cognitive-behavioral therapy (iCBT) condition (n=40). Participants in the AMP+FACT group experienced greater reductions in social anxiety symptoms than both active (n=40) and control (n=39) groups reported by Carlbring et al., and did not differ in symptom reductions from the iCBT group. Higher attention bias predicted greater symptom reductions for participants who completed AMP, but not for the control group. Moreover, change in attention bias mediated the relationship between AMP group (active condition reported by Carlbring et al. versus AMP+FACT) and change in social anxiety symptoms. These results suggest the importance of interpreting findings related to symptom change in attention training studies in the context of bias effects.
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| 435. |
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| 436. |
- Chou, Shao-wei, et al.
(författare)
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Collective Deceleration of Laser-Driven Electron Bunches
- 2016
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 117:14
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Tidskriftsartikel (refereegranskat)abstract
- Few-fs electron bunches from laser wakefield acceleration (LWFA) can efficiently drive plasma wakefields (PWFs), as shown by their propagation through underdense plasma in two experiments. A strong and density-insensitive deceleration of the bunches has been observed in 2 mm of 1018 cm−3 density plasma with 5.1 GV=m average gradient, which is attributed to a self-driven PWF. This observation implies that the physics of PWFs, usually relying on large-scale rf accelerators as drivers, can be studied by tabletop LWFA electron sources.
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| 437. |
- Cuijpers, P., et al.
(författare)
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Comparison of psychotherapies for adult depression to pill placebo control groups: a meta-analysis
- 2014
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Ingår i: Psychological Medicine. - : Cambridge University Press (CUP). - 0033-2917 .- 1469-8978. ; 44:4, s. 685-695
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Forskningsöversikt (refereegranskat)abstract
- Background The effects of antidepressants for treating depressive disorders have been overestimated because of selective publication of positive trials. Reanalyses that include unpublished trials have yielded reduced effect sizes. This in turn has led to claims that antidepressants have clinically insignificant advantages over placebo and that psychotherapy is therefore a better alternative. To test this, we conducted a meta-analysis of studies comparing psychotherapy with pill placebo. Method Ten 10 studies comparing psychotherapies with pill placebo were identified. In total, 1240 patients were included in these studies. For each study, Hedges g was calculated. Characteristics of the studies were extracted for subgroup and meta-regression analyses. Results The effect of psychotherapy compared to pill placebo at post-test was g=0.25 [95% confidence interval (CI) 0.14-0.36, I (2)=0%, 95% CI 0-58]. This effect size corresponds to a number needed to treat (NNT) of 7.14 (95% CI 5.00-12.82). The psychotherapy conditions scored 2.66 points lower on the Hamilton Depression Rating Scale (HAMD) than the placebo conditions, and 3.20 points lower on the Beck Depression Inventory (BDI). Some indications for publication bias were found (two missing studies). We found no significant differences between subgroups of the studies and in meta-regression analyses we found no significant association between baseline severity and effect size. Conclusions Although there are differences between the role of placebo in psychotherapy and pharmacotherapy research, psychotherapy has an effect size that is comparable to that of antidepressant medications. Whether these effects should be deemed clinically relevant remains open to debate.
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| 438. |
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| 439. |
- Felipe, T., et al.
(författare)
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Three-dimensional structure of a sunspot light bridge
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 596
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Tidskriftsartikel (refereegranskat)abstract
- Context. Active regions are the most prominent manifestations of solar magnetic fields; their generation and dissipation are fundamental problems in solar physics. Light bridges are commonly present during sunspot decay, but a comprehensive picture of their role in the removal of the photospheric magnetic field is still lacking. Aims. We study the three-dimensional configuration of a sunspot, and in particular, its light bridge, during one of the last stages of its decay. Methods. We present the magnetic and thermodynamical stratification inferred from full Stokes inversions of the photospheric Si I 10 827 angstrom and Ca I 10 839 angstrom lines obtained with the GREGOR Infrared Spectrograph of the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The analysis is complemented by a study of continuum images covering the disk passage of the active region, which are provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Results. The sunspot shows a light bridge with penumbral continuum intensity that separates the central umbra from a smaller umbra. We find that in this region the magnetic field lines form a canopy with lower magnetic field strength in the inner part. The photospheric light bridge is dominated by gas pressure (high-beta), as opposed to the surrounding umbra, where the magnetic pressure is higher. A convective flow is observed in the light bridge. This flow is able to bend the magnetic field lines and to produce field reversals. The field lines merge above the light bridge and become as vertical and strong as in the surrounding umbra. We conclude that this occurs because two highly magnetized regions approach each other during the sunspot evolution.
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| 440. |
- Fernández-Pello, Sergio, et al.
(författare)
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A Systematic Review and Meta-analysis Comparing the Effectiveness and Adverse Effects of Different Systemic Treatments for Non-clear Cell Renal Cell Carcinoma
- 2017
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Ingår i: European Urology. - : Elsevier BV. - 0302-2838 .- 1873-7560. ; 71:3, s. 426-436
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Forskningsöversikt (refereegranskat)abstract
- Context While vascular endothelial growth factor-targeted therapy and mammalian target of rapamycin inhibition are effective strategies in treating clear cell renal cell carcinoma (ccRCC), the most effective therapeutic approach for patients with non-clear cell RCC (non-ccRCC) is unknown. Objective To systematically review relevant literature comparing the oncological outcomes and adverse events of different systemic therapies for patients with metastatic non-ccRCC. Evidence acquisition Relevant databases including MEDLINE, Embase, and the Cochrane Library were searched up to March 24, 2016. Only comparative studies were included. Risk of bias and confounding assessments were performed. A meta-analysis was planned for and only performed if methodologically appropriate; otherwise, a narrative synthesis was undertaken. Evidence synthesis The literature search identified 812 potential titles and abstracts. Five randomized controlled trials, recruiting a total of 365 patients, were included. Three studies compared sunitinib against everolimus, one of which reported the results for non-ccRCC as a subgroup rather than as an entire randomized cohort. Individually, the studies showed a trend towards favoring sunitinib in terms of overall survival and progression-free survival (PFS; Everolimus versus Sunitinib in Patients with Metastatic Non-clear Cell Renal Cell Carcinoma hazard ratio [HR]: 1.41, 80% confidence interval [CI] 1.03–1.92 and 1.41, 95% CI: 0.88–2.27, Evaluation in Metastatic Non-clear Cell Renal Cell Carcinoma HR: 1.16, 95% CI: 0.67–2.01, Efficacy and Safety Comparison of RAD001 Versus Sunitinib in the First-line and Second-line Treatment of Patients with Metastatic Renal Cell Carcinoma HR: 1.5, 95% CI: 0.9–2.8), but this trend did not reach statistical significance in any study. Meta-analysis was performed on two studies which solely recruited patients with non-ccRCC reporting on PFS, the results of which were inconclusive (HR: 1.30, 95% CI: 0.91–1.86). Sunitinib was associated with more Grade 3–4 adverse events than everolimus, although this was not statistically significant. Conclusions This systematic review and meta-analysis represent a robust summary of the evidence base for systemic treatment of metastatic non-ccRCC. The results show a trend towards favoring vascular endothelial growth factor-targeted therapy for PFS and overall survival compared with mammalian target of rapamycin inhibitors, although statistical significance was not reached. The relative benefits and harms of these treatments remain uncertain. Further research, either in the form of an individual patient data meta-analysis involving all relevant trials, or a randomized controlled trial with sufficient power to detect potential differences between treatments, is needed. Patient summary We examined the literature to determine the most effective treatments for advanced kidney cancer patients whose tumors are not of the clear cell subtype. The results suggest that a drug called sunitinib might be more effective than everolimus, but the statistics supporting this statement are not yet entirely reliable. Further research is required to clarify this unmet medical need.
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