2,125 research outputs found
Fermi-Edge Superfluorescence from a Quantum-Degenerate Electron-Hole Gas
We report on the observation of spontaneous bursts of coherent radiation from
a quantum-degenerate gas of nonequilibrium electron-hole pairs in semiconductor
quantum wells. Unlike typical spontaneous emission from semiconductors, which
occurs at the band edge, the observed emission occurs at the quasi-Fermi edge
of the carrier distribution. As the carriers are consumed by recombination, the
quasi-Fermi energy goes down toward the band edge, and we observe a
continuously red-shifting streak. We interpret this emission as cooperative
spontaneous recombination of electron-hole pairs, or superfluorescence, which
is enhanced by Coulomb interactions near the Fermi edge. This novel many-body
enhancement allows the magnitude of the spontaneously developed macroscopic
polarization to exceed the maximum value for ordinary superfluorescence, making
electron-hole superfluorescence even more "super" than atomic
superfluorescence.Comment: 10 pages, 5 figure
Micromachined “side-viewing” optical sensor probe for detection of esophageal cancers
In this paper, we report the design, fabrication and testing of a new miniaturized optical sensor probe with “side viewing” capability for oblique incidence diffuse reflectance spectrometry. The sensor probe consists of a lithographically patterned polymer waveguides chip and two micromachined positioning substrates and source/collection fibers to achieve 45° light incidence and collection of spatially resolved diffuse reflectance. Diffuse reflectance of human esophageal surface has been successfully measured for differentiation of cancerous tissues from normal ones
Collective Antenna Effects in the Terahertz and Infrared Response of Highly Aligned Carbon Nanotube Arrays
We study macroscopically-aligned single-wall carbon nanotube arrays with
uniform lengths via polarization-dependent terahertz and infrared transmission
spectroscopy. Polarization anisotropy is extreme at frequencies less than
3 THz with no sign of attenuation when the polarization is perpendicular
to the alignment direction. The attenuation for both parallel and perpendicular
polarizations increases with increasing frequency, exhibiting a pronounced and
broad peak around 10 THz in the parallel case. We model the electromagnetic
response of the sample by taking into account both radiative scattering and
absorption losses. We show that our sample acts as an effective antenna due to
the high degree of alignment, exhibiting much larger radiative scattering than
absorption in the mid/far-infrared range. Our calculated attenuation spectrum
clearly shows a non-Drude peak at 10 THz in agreement with the
experiment.Comment: 5 pages, 5 figure
Optimization of broadband semiconductor chirped mirrors with genetic algorithm
Genetic algorithm was applied for optimization
of dispersion properties in semiconductor Bragg reflectors
for applications in femtosecond lasers. Broadband,
large negative group-delay dispersion was achieved in the
optimized design: The group-delay dispersion (GDD) as
large as −3500 fs2
was theoretically obtained over a 10-nm
bandwidth. The designed structure was manufactured and
tested, providing GDD −3320 fs2
over a 7-nm bandwidth.
The mirror performance was verified in semiconductor
structures grown with molecular beam epitaxy. The mirror
was tested in a passively mode-locked Yb:KYW laser
Fault-Tolerant Exact State Transmission
We show that a category of one-dimensional XY-type models may enable
high-fidelity quantum state transmissions, regardless of details of coupling
configurations. This observation leads to a fault- tolerant design of a state
transmission setup. The setup is fault-tolerant, with specified thresholds,
against engineering failures of coupling configurations, fabrication
imperfections or defects, and even time-dependent noises. We propose the
implementation of the fault-tolerant scheme using hard-core bosons in
one-dimensional optical lattices.Comment: 5 pages and 4 figure
Electronic structure, magnetism, and disorder in the Heusler compound CoTiSn
Polycrystalline samples of the half-metallic ferromagnet Heusler compound
CoTiSn have been prepared and studied using bulk techniques (X-ray
diffraction and magnetization) as well as local probes (Sn M\"ossbauer
spectroscopy and Co nuclear magnetic resonance spectroscopy) in order to
determine how disorder affects half-metallic behavior and also, to establish
the joint use of M\"ossbauer and NMR spectroscopies as a quantitative probe of
local ion ordering in these compounds. Additionally, density functional
electronic structure calculations on ordered and partially disordered
CoTiSn compounds have been carried out at a number of different levels of
theory in order to simultaneously understand how the particular choice of DFT
scheme as well as disorder affect the computed magnetization. Our studies
suggest that a sample which seems well-ordered by X-ray diffraction and
magnetization measurements can possess up to 10% of antisite (Co/Ti)
disordering. Computations similarly suggest that even 12.5% antisite Co/Ti
disorder does not destroy the half-metallic character of this material.
However, the use of an appropriate level of non-local DFT is crucial.Comment: 11 pages and 5 figure
De novo variants disturbing the transactivation capacity of POU3F3 cause a characteristic neurodevelopmental disorder
POU3F3, also referred to as Brain-1, is a well-known transcription factor involved in the development of the central nervous system, but it has not previously been associated with a neurodevelopmental disorder. Here, we report the identification of 19 individuals with heterozygous POU3F3 disruptions, most of which are de novo variants. All individuals had developmental delays and/or intellectual disability and impairments in speech and language skills. Thirteen individuals had characteristic low-set, prominent, and/or cupped ears. Brain abnormalities were observed in seven of eleven MRI reports. POU3F3 is an intronless gene, insensitive to nonsense-mediated decay, and 13 individuals carried protein-truncating variants. All truncating variants that we tested in cellular models led to aberrant subcellular localization of the encoded protein. Luciferase assays demonstrated negative effects of these alleles on transcriptional activation of a reporter with a FOXP2-derived binding motif. In addition to the loss-of-function variants, five individuals had missense variants that clustered at specific positions within the functional domains, and one small in-frame deletion was identified. Two missense variants showed reduced transactivation capacity in our assays, whereas one variant displayed gain-of-function effects, suggesting a distinct pathophysiological mechanism. In bioluminescence resonance energy transfer (BRET) interaction assays, all the truncated POU3F3 versions that we tested had significantly impaired dimerization capacities, whereas all missense variants showed unaffected dimerization with wild-type POU3F3. Taken together, our identification and functional cell-based analyses of pathogenic variants in POU3F3, coupled with a clinical characterization, implicate disruptions of this gene in a characteristic neurodevelopmental disorder
Genetic markers of Munc13 protein family member, BAIAP3, are gender-specifically associated with anxiety and benzodiazepine abuse in mouse and man
Anxiety disorders and substance abuse, including benzodiazepine use disorder, frequently occur together. Unfortunately, treatment of anxiety disorders still includes benzodiazepines, and patients with an existing comorbid benzodiazepine use disorder or a genetic susceptibility for benzodiazepine use disorder may be at risk of adverse treatment outcomes. The identification of genetic predictors for anxiety disorders, and especially for benzodiazepine use disorder, could aid the selection of the best treatment option and improve clinical outcomes. The brain-specific angiogenesis inhibitor I–associated protein 3 (Baiap3) is a member of the mammalian uncoordinated 13 (Munc13) protein family of synaptic regulators of neurotransmitter exocytosis, with a striking expression pattern in amygdalae, hypothalamus and periaqueductal gray. Deletion of Baiap3 in mice leads to enhanced seizure propensity and increased anxiety, with the latter being more pronounced in female than in male animals. We hypothesized that genetic variation in human BAIAP3 may also be associated with anxiety. By using a phenotype-based genetic association study, we identified two human BAIAP3 single-nucleotide polymorphism risk genotypes (AA for rs2235632, TT for rs1132358) that show a significant association with anxiety in women and, surprisingly, with benzodiazepine abuse in men. Returning to mice, we found that male, but not female, Baiap3 knockout (KO) mice develop tolerance to diazepam more quickly than control animals. Analysis of cultured Baiap3 KO hypothalamus slices revealed an increase in basal network activity and an altered response to diazepam withdrawal. Thus, Baiap3/BAIAP3 is gender specifically associated with anxiety and benzodiazepine use disorder, and the analysis of Baiap3/BAIAP3-related functions may help elucidate mechanisms underlying the development of both disorders
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