2,057 research outputs found
Energy levels of a parabolically confined quantum dot in the presence of spin-orbit interaction
We present a theoretical study of the energy levels in a parabolically
confined quantum dot in the presence of the Rashba spin-orbit interaction
(SOI). The features of some low-lying states in various strengths of the SOI
are examined at finite magnetic fields. The presence of a magnetic field
enhances the possibility of the spin polarization and the SOI leads to
different energy dependence on magnetic fields applied. Furthermore, in high
magnetic fields, the spectra of low-lying states show basic features of
Fock-Darwin levels as well as Landau levels.Comment: 6 pages, 4 figures, accepted by J. Appl. Phy
Instrumentation of a high-sensitivity microwave vector detection system for low-temperature applications
We present the design and the circuit details of a high-sensitivity microwave
vector detection system, which is aiming for studying the low-dimensional
electron system embedded in the slots of a coplanar waveguide at low
temperatures. The coplanar waveguide sample is placed inside a phase-locked
loop; the phase change of the sample may cause a corresponding change in the
operation frequency, which can be measured precisely. We also employ a
double-pulse modulation on the microwave signals, which comprises a fast pulse
modulation for gated averaging and a slow pulse modulation for lock-in
detection. In measurements on real samples at low temperatures, this system
provides much better resolutions in both amplitude and phase than most of the
conventional vector analyzers at power levels below -65 dBm.Comment: 7 pages, 11 figures, 1 table, lette
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Medical students' comfort levels with performing the basic head and neck examination in practice: follow-up during the core clerkship year.
ObjectiveFollowing our preliminary study on junior medical students' comfort levels in performing the head and neck physical examination (H&NPE) before and after a department-led teaching session, we assessed the longitudinal effect of this session on students during the core clinical clerkship year, in which these skills were performed on real patients.DesignAnonymous cross-sectional survey study as a follow-up to previous intervention.MethodsOverall, 101 and 90 second-year medical students participated in an H&NPE teaching session 1 year before the current survey administration in 2 consecutive years. The same cohorts of students, as third years, were asked to rate their comfort levels (0-5-point Likert scale) in performing the H&NPE and the importance of otolaryngology rotations in medical school and primary care residency training.ResultsOf the 101 and 90 students, 53 and 46 medical students completed the follow-up survey in each respective year. For both classes, compared with before the teaching session, students reported an average comfort level of 2.8 (somewhat to moderately comfortable) in performing the complete H&NPE (p < 0.0001) during the core clinical clerkship year. Similar changes were observed for the individual ear, nose, mouth, and neck components of the examination (all p's < 0.0002). Students at follow-up reported statistically similar comfort levels when compared with immediately after the teaching session for the ear, oral cavity, and neck examinations.ConclusionThe initial teaching session persistently improved medical students' comfort levels in performing the H&NPE, with some attrition in comfort levels with performing the nasal examination and complete H&NPE. An otolaryngologist-directed, practical educational intervention may permanently reinforce the acquisition of complex skills such as the H&NPE
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Complete response of skull base inverted papilloma to chemotherapy: Case report.
BackgroundInverted papilloma (IP) is the most common benign sinonasal neoplasm. Endoscopic techniques, improved understanding of pathophysiology, and novel surgical approaches have allowed rhinologists to treat IPs more effectively, with surgery being the mainstay of therapy. Frontal sinus IP poses a challenge for surgical therapy due to complex anatomy and potentially difficult surgical access.ObjectivesWe reported a unique case of a massive frontal sinus IP that presented with intracranial and orbital extension, with near resolution after chemotherapy.MethodsA retrospective case review of a patient with a frontal sinus IP treated at a tertiary academic medical center.ResultsA 75-year-old male patient presented with nasal obstruction, purulent nasal discharge, and a growing left supraorbital mass. Endoscopy demonstrated a mass that filled both frontal and ethmoid sinuses, with orbital invasion. There also was substantial erosion of the posterior table, which measured 1.73 × 1.40 cm. A biopsy specimen demonstrated IP with carcinoma in situ. The patient was deemed unresectable on initial evaluation and, subsequently, underwent chemotherapy (carboplatin and paclitaxel). The tumor had a dramatic response to chemotherapy, and the patient elected for definitive surgery to remove any residual disease. During surgery, only a small focus of IP was found along the superior wall of the frontal sinus. No tumor was found elsewhere, including at the site of skull base erosion. The final pathology was IP without carcinoma in situ or dysplasia.ConclusionThis was the first reported case of chemotherapeutic "debulking" of IP, which facilitated surgical resection, despite substantial intracranial and orbital involvement. Although nearly all IPs can be treated surgically, rare cases, such as unresectable tumors, may benefit from systemic chemotherapy
AMPA Receptor Phosphorylation and Synaptic Colocalization on Motor Neurons Drive Maladaptive Plasticity below Complete Spinal Cord Injury.
Clinical spinal cord injury (SCI) is accompanied by comorbid peripheral injury in 47% of patients. Human and animal modeling data have shown that painful peripheral injuries undermine long-term recovery of locomotion through unknown mechanisms. Peripheral nociceptive stimuli induce maladaptive synaptic plasticity in dorsal horn sensory systems through AMPA receptor (AMPAR) phosphorylation and trafficking to synapses. Here we test whether ventral horn motor neurons in rats demonstrate similar experience-dependent maladaptive plasticity below a complete SCI in vivo. Quantitative biochemistry demonstrated that intermittent nociceptive stimulation (INS) rapidly and selectively increases AMPAR subunit GluA1 serine 831 phosphorylation and localization to synapses in the injured spinal cord, while reducing synaptic GluA2. These changes predict motor dysfunction in the absence of cell death signaling, suggesting an opportunity for therapeutic reversal. Automated confocal time-course analysis of lumbar ventral horn motor neurons confirmed a time-dependent increase in synaptic GluA1 with concurrent decrease in synaptic GluA2. Optical fractionation of neuronal plasma membranes revealed GluA2 removal from extrasynaptic sites on motor neurons early after INS followed by removal from synapses 2 h later. As GluA2-lacking AMPARs are canonical calcium-permeable AMPARs (CP-AMPARs), their stimulus- and time-dependent insertion provides a therapeutic target for limiting calcium-dependent dynamic maladaptive plasticity after SCI. Confirming this, a selective CP-AMPAR antagonist protected against INS-induced maladaptive spinal plasticity, restoring adaptive motor responses on a sensorimotor spinal training task. These findings highlight the critical involvement of AMPARs in experience-dependent spinal cord plasticity after injury and provide a pharmacologically targetable synaptic mechanism by which early postinjury experience shapes motor plasticity
Non-Markovian entanglement dynamics of quantum continuous variable systems in thermal environments
We study two continuous variable systems (or two harmonic oscillators) and
investigate their entanglement evolution under the influence of non-Markovian
thermal environments. The continuous variable systems could be two modes of
electromagnetic fields or two nanomechanical oscillators in the quantum domain.
We use quantum open system method to derive the non-Markovian master equations
of the reduced density matrix for two different but related models of the
continuous variable systems. The two models both consist of two interacting
harmonic oscillators. In model A, each of the two oscillators is coupled to its
own independent thermal reservoir, while in model B the two oscillators are
coupled to a common reservoir. To quantify the degrees of entanglement for the
bipartite continuous variable systems in Gaussian states, logarithmic
negativity is used. We find that the dynamics of the quantum entanglement is
sensitive to the initial states, the oscillator-oscillator interaction, the
oscillator-environment interaction and the coupling to a common bath or to
different, independent baths.Comment: 10 two-column pages, 8 figures, to appear in Phys. Rev.
The Immitigable Nature of Assembly Bias: The Impact of Halo Definition on Assembly Bias
Dark matter halo clustering depends not only on halo mass, but also on other
properties such as concentration and shape. This phenomenon is known broadly as
assembly bias. We explore the dependence of assembly bias on halo definition,
parametrized by spherical overdensity parameter, . We summarize the
strength of concentration-, shape-, and spin-dependent halo clustering as a
function of halo mass and halo definition. Concentration-dependent clustering
depends strongly on mass at all . For conventional halo definitions
(), concentration-dependent clustering
at low mass is driven by a population of haloes that is altered through
interactions with neighbouring haloes. Concentration-dependent clustering can
be greatly reduced through a mass-dependent halo definition with for haloes with . Smaller implies larger radii and
mitigates assembly bias at low mass by subsuming altered, so-called backsplash
haloes into now larger host haloes. At higher masses () larger overdensities, , are necessary. Shape- and spin-dependent clustering are
significant for all halo definitions that we explore and exhibit a relatively
weaker mass dependence. Generally, both the strength and the sense of assembly
bias depend on halo definition, varying significantly even among common
definitions. We identify no halo definition that mitigates all manifestations
of assembly bias. A halo definition that mitigates assembly bias based on one
halo property (e.g., concentration) must be mass dependent. The halo
definitions that best mitigate concentration-dependent halo clustering do not
coincide with the expected average splashback radii at fixed halo mass.Comment: 19 pages, 13 figures. Updated to published version. Main result
summarized in Figure 1
Angular position of nodes in the superconducting gap of YBCO
The thermal conductivity of a YBCO single crystal has been studied as a
function of the relative orientation of the crystal axes and a magnetic field
rotating in the Cu-O planes. Measurements were carried out at several
temperatures below T_c and at a fixed field of 30 kOe. A four-fold symmetry
characteristic of a superconducting gap with nodes at odd multiples of 45
degrees in k-space was resolved. Experiments were performed to exclude a
possible macroscopic origin for such a four-fold symmetry such as sample shape
or anisotropic pinning. Our results impose an upper limit of 10% on the weight
of the s-wave component of the essentially d-wave superconducting order
parameter of YBCO.Comment: 10 pages, 4 figure
Structural Change in (Economic) Time Series
Methods for detecting structural changes, or change points, in time series
data are widely used in many fields of science and engineering. This chapter
sketches some basic methods for the analysis of structural changes in time
series data. The exposition is confined to retrospective methods for univariate
time series. Several recent methods for dating structural changes are compared
using a time series of oil prices spanning more than 60 years. The methods
broadly agree for the first part of the series up to the mid-1980s, for which
changes are associated with major historical events, but provide somewhat
different solutions thereafter, reflecting a gradual increase in oil prices
that is not well described by a step function. As a further illustration, 1990s
data on the volatility of the Hang Seng stock market index are reanalyzed.Comment: 12 pages, 6 figure
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