17,215 research outputs found
Direct microwave measurement of Andreev-bound-state dynamics in a proximitized semiconducting nanowire
The modern understanding of the Josephson effect in mesosopic devices derives
from the physics of Andreev bound states, fermionic modes that are localized in
a superconducting weak link. Recently, Josephson junctions constructed using
semiconducting nanowires have led to the realization of superconducting qubits
with gate-tunable Josephson energies. We have used a microwave circuit QED
architecture to detect Andreev bound states in such a gate-tunable junction
based on an aluminum-proximitized InAs nanowire. We demonstrate coherent
manipulation of these bound states, and track the bound-state fermion parity in
real time. Individual parity-switching events due to non-equilibrium
quasiparticles are observed with a characteristic timescale . The of a topological nanowire
junction sets a lower bound on the bandwidth required for control of Majorana
bound states
A hierarchy of linguistic predictions during natural language comprehension
Understanding spoken language requires transforming ambiguous acoustic streams into a hierarchy of representations, from phonemes to meaning. It has been suggested that the brain uses prediction to guide the interpretation of incoming input. However, the role of prediction in language processing remains disputed, with disagreement about both the ubiquity and representational nature of predictions. Here, we address both issues by analyzing brain recordings of participants listening to audiobooks, and using a deep neural network (GPT-2) to precisely quantify contextual predictions. First, we establish that brain responses to words are modulated by ubiquitous predictions. Next, we disentangle model-based predictions into distinct dimensions, revealing dissociable neural signatures of predictions about syntactic category (parts of speech), phonemes, and semantics. Finally, we show that high-level (word) predictions inform low-level (phoneme) predictions, supporting hierarchical predictive processing. Together, these results underscore the ubiquity of prediction in language processing, showing that the brain spontaneously predicts upcoming language at multiple levels of abstraction
History of childbirths relates to region-specific brain aging patterns in middle and older-aged women
Pregnancy involves maternal brain adaptations, but little is known about how parity influences women’s brain aging trajectories later in life. In this study, we replicated previous findings showing less apparent brain aging in women with a history of childbirths, and identified regional brain aging patterns linked to parity in 19,787 middle and older-aged women. Using novel applications of brain-age prediction methods, we found that a higher number of previous childbirths was linked to less apparent brain aging in striatal and limbic regions. The strongest effect was found in the accumbens – a key region in the mesolimbic reward system, which plays an important role in maternal behavior. While only prospective longitudinal studies would be conclusive, our findings indicate that subcortical brain modulations during pregnancy and postpartum may be traceable decades after childbirth
IF impedance and mixer gain of NbN hot electron bolometers
The intermediate frequency (IF) characteristics, the frequency dependent IF impedance, and the mixer conversion gain of a small area hot electron bolometer (HEB) have been measured and modeled. The device used is a twin slot antenna coupled NbN HEB mixer with a bridge area of 1×0.15 µm^2, and a critical temperature of 8.3 K. In the experiment the local oscillator frequency was 1.300 THz, and the (IF) 0.05–10 GHz. We find that the measured data can be described in a self-consistent manner with a thin film model presented by Nebosis et al. [Proceedings of the Seventh International Symposium on Space Terahertz Technology, Charlottesville, VA, 1996 (unpublished), pp. 601–613], that is based on the two temperature electron-phonon heat balance equations of Perrin-Vanneste [J. Phys. (Paris) 48, 1311 (1987)]. From these results the thermal time constant, governing the gain bandwidth of HEB mixers, is observed to be a function of the electron-phonon scattering time, phonon escape time, and the electron temperature. From the developed theory the maximum predicted gain bandwidth for a NbN HEB is found to be 5.5–6 GHz. In contrast, the gain bandwidth of the device under discussion was measured to be ~2.3 GHz which, consistent with the outlined theory, is attributed to a somewhat low critical temperature and nonoptimal film thickness (6 nm)
Observation of Andreev Reflection Enhanced Shot Noise
We have experimentally investigated the quasiparticle shot noise in
NbN/MgO/NbN superconductor - insulator - superconductor tunnel junctions. The
observed shot noise is significantly larger than theoretically expected. We
attribute this to the occurrence of multiple Andreev reflection processes in
pinholes present in the MgO barrier. This mechanism causes the current to flow
in large charge quanta (Andreev clusters), with a voltage dependent average
value of m = 1+ 2 Delta/eV times the electron charge. Because of this charge
enhancement effect, the shot noise is increased by the factor m.Comment: 4 pages, 5 figures include
Level of arterial ligation in total mesorectal excision (TME): an anatomical study
Introduction: High-tie ligation is a common practice in rectal cancer surgery. However, it compromises perfusion of the proximal limb of the anastomosis. This anatomical study was designed to assess the value of low-tie ligation in order to obtain a tension-free anastomosis. Materials and methods: Consecutive high- and low-tie resections were performed on 15 formalin-fixed specimens, with or without splenic flexure mobilization. If the proximal colon limb could reach the superior aspect of the symphysis pubis with more than 3 cm, the limb would be long enough for a tension-free colorectal anastomosis. Results: In 80% of cases, it was not necessary to perform high-tie ligation as sufficient length was gained with low-tie ligation. The descending branch of the left colic artery was the limiting factor in the other 20% of cases. Resecting half the sigmoid resulted in four times as many tension-free anastomoses after low-tie resection. Conclusion: In the majority of cases, it was not necessary to perform high-tie ligation in order to create a tension-free anastomosis. Low-tie ligation was applicable in 80% of cases and might prevent anastomotic leakage due to insufficient blood supply of the proximal colon limb
Structure, gating and interactions of the voltage-dependent anion channel
The voltage-dependent anion channel (VDAC) is one of the most highly abundant proteins found in the outer mitochondrial membrane, and was one of the earliest discovered. Here we review progress in understanding VDAC function with a focus on its structure, discussing various models proposed for voltage gating as well as potential drug targets to modulate the channel’s function. In addition, we explore the sensitivity of VDAC structure to variations in the membrane environment, comparing DMPC-only, DMPC with cholesterol, and near-native lipid compositions, and use magic-angle spinning NMR spectroscopy to locate cholesterol on the outside of the β-barrel. We find that the VDAC protein structure remains unchanged in different membrane compositions, including conditions with cholesterol
Continuous monitoring of a trapped, superconducting spin
Readout and control of fermionic spins in solid-state systems are key
primitives of quantum information processing and microscopic magnetic sensing.
The highly localized nature of most fermionic spins decouples them from
parasitic degrees of freedom, but makes long-range interoperability difficult
to achieve. In light of this challenge, an active effort is underway to
integrate fermionic spins with circuit quantum electrodynamics (cQED), which
was originally developed in the field of superconducting qubits to achieve
single-shot, quantum-non-demolition (QND) measurements and long-range
couplings. However, single-shot readout of an individual spin with cQED has
remained elusive due to the difficulty of coupling a resonator to a particle
trapped by a charge-confining potential. Here we demonstrate the first
single-shot, cQED readout of a single spin. In our novel implementation, the
spin is that of an individual superconducting quasiparticle trapped in the
Andreev levels of a semiconductor nanowire Josephson element. Due to a
spin-orbit interaction inside the nanowire, this "superconducting spin"
directly determines the flow of supercurrent through the element. We harnessed
this spin-dependent supercurrent to achieve both a zero-field spin splitting as
well as a long-range interaction between the quasiparticle and a
superconducting microwave resonator. Owing to the strength of this interaction
in our device, measuring the resultant spin-dependent resonator frequency
yielded QND spin readout with 92% fidelity in 1.9 s and allowed us to
monitor the quasiparticle's spin in real time. These results pave the way for
new "fermionic cQED" devices: superconducting spin qubits operating at zero
magnetic field, devices in which the spin has enhanced governance over the
circuit, and time-domain measurements of Majorana modes
Mental rotation task of hands: differential influence number of rotational axes
Various studies on the hand laterality judgment task, using complex sets of stimuli, have shown that the judgments during this task are dependent on bodily constraints. More specific, these studies showed that reaction times are dependent on the participant’s posture or differ for hand pictures rotated away or toward the mid-sagittal plane (i.e., lateral or medial rotation, respectively). These findings point to the use of a cognitive embodied process referred to as motor imagery. We hypothesize that the number of axes of rotation of the displayed stimuli during the task is a critical factor for showing engagement in a mental rotation task, with an increased number of rotational axes leading to a facilitation of motor imagery. To test this hypothesis, we used a hand laterality judgment paradigm in which we manipulated the difficulty of the task via the manipulation of the number of rotational axes of the shown stimuli. Our results showed increased influence of bodily constraints for increasing number of axes of rotation. More specifically, for the stimulus set containing stimuli rotated over a single axis, no influence of biomechanical constraints was present. The stimulus sets containing stimuli rotated over more than one axes of rotation did induce the use of motor imagery, as a clear influence of bodily constraints on the reaction times was found. These findings extend and refine previous findings on motor imagery as our results show that engagement in motor imagery critically depends on the used number of axes of rotation of the stimulus set
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