1,772 research outputs found
Flux through a hole from a shaken granular medium
We have measured the flux of grains from a hole in the bottom of a shaken
container of grains. We find that the peak velocity of the vibration, vmax,
controls the flux, i.e., the flux is nearly independent of the frequency and
acceleration amplitude for a given value of vmax. The flux decreases with
increasing peak velocity and then becomes almost constant for the largest
values of vmax. The data at low peak velocity can be quantitatively described
by a simple model, but the crossover to nearly constant flux at larger peak
velocity suggests a regime in which the granular density near the container
bottom is independent of the energy input to the system.Comment: 14 pages, 4 figures. to appear in Physical Review
Impurity Band Conduction in a High Temperature Ferromagnetic Semiconductor
The band structure of a prototypical dilute ferromagnetic semiconductor,
GaMnAs, is studied across the phase diagram via optical
spectroscopy. We prove that the Fermi energy () resides in a Mn induced
impurity band (IB). This conclusion is based upon careful analysis of the
frequency and temperature dependence of the optical conductivity
(). From our analysis of we infer
a large effective mass () of the carriers, supporting the view that
conduction occurs in an IB. Our results also provide useful insights into the
transport properties of Mn-doped GaAs.Comment: 4 pages, 4 figure
Quantum planes and quantum cylinders from Poisson homogeneous spaces
Quantum planes and a new quantum cylinder are obtained as quantization of
Poisson homogeneous spaces of two different Poisson structures on classical
Euclidean group E(2).Comment: 13 pages, plain Tex, no figure
Intraoperative positioning related injury of superficial radial nerve after shoulder arthroscopy – a rare iatrogenic injury: a case report
Arthroscopy of the shoulder is a well-established and routine procedure. The role is expected to increase further with an ever-increasing list of indications reflecting the gratifying results. Intraoperative injuries of nerves related to positioning are known but, fortunately, rare with shoulder arthroscopy. Appropriate assessment of patient and careful positioning is paramount in prevention of these injuries. Despite robust preventive measures, these injuries continue to occur from time to time. Although there are few reports of position-related intraoperative nerve injuries associated with shoulder arthroscopy, the involvement of superficial radial nerve (SRN) has never been described before. We report a rare case of positioning related injury of SRN in a 35-year-old female after arthroscopic rotator cuff repair and discuss the preventive and legal aspects. To authors' knowledge this is the first reported case of intraoperative positioning related injury of SRN
Stochastic Ballistic Annihilation and Coalescence
We study a class of stochastic ballistic annihilation and coalescence models
with a binary velocity distribution in one dimension. We obtain an exact
solution for the density which reveals a universal phase diagram for the
asymptotic density decay. By universal we mean that all models in the class are
described by a single phase diagram spanned by two reduced parameters. The
phase diagram reveals four regimes, two of which contain the previously studied
cases of ballistic annihilation. The two new phases are a direct consequence of
the stochasticity. The solution is obtained through a matrix product approach
and builds on properties of a q-deformed harmonic oscillator algebra.Comment: 4 pages RevTeX, 3 figures; revised version with some corrections,
additional discussion and in RevTeX forma
Quartic scaling of sound attenuation with frequency in vitreous silica
Several theoretical approaches to disordered media predict that acoustic
waves should undergo a quartic increase in their attenuation coefficient with
increasing frequency in the sub-terahertz region. Such Rayleigh-type scattering
would be related to the anomalous low-temperature plateau in the thermal
conductivity and to the so-called boson peak, i.e. an excess of vibrational
modes above the Debye density of states at around 1 THz. Brillouin scattering
of light allows the measurement of sound absorption and velocity dispersion up
to about 0.1 THz while inelastic x-ray scattering is limited to frequencies
larger than about 1 THz. We take advantage of the advent of ultrafast optical
techniques to explore the acoustical properties of amorphous SiO2 layers in the
difficult but crucial frequency region within this gap. A quartic scaling law
with frequency is clearly revealed between 0.2 and 0.9 THz, which is further
shown to be independent of temperature. This strongly damped regime is
accompanied by a decrease in the sound velocity already starting from about 0.5
THz, in line with theories. Our study assists to clarify the anomalous
acoustical properties in glasses at frequencies entering the boson peak region.Comment: 4 figures, 11 page
Changes in intracellular ion activities induced by adrenaline in human and rat skeletal muscle
To study the stimulating effect of adrenaline (ADR) on active Na+/K+ transport we used double-barrelled ion-sensitive micro-electrodes to measure the activities of extracellular K+ (aKe) and intracellular Na+ (aNai) in isolated preparations of rat soleus muscle, normal human intercostal muscle and one case of hyperkalemic periodic paralysis (h.p.p.). In these preparations bath-application of ADR (10−6 M) resulted in a membrane hyperpolarization and transient decreasesaKe andaNai which could be blocked by ouabain (3×10−4 M). In the h.p.p. muslce a continuous rise ofaNai induced by elevation ofaKe to 5.2 mM could be stopped by ADR. In addition, the intracellular K+ activity (aKi), the free intracellular Ca2+ concentration (pCai) and intracellular pH (pHi) were monitored in rat soleus muscle. During ADRaKi increased, pHi remained constant and intracellular Ca2+ apparently decreased. In conclusion, our data show that ADR primarily stimulates the Na+/K+ pump in mammalian skeletal muscle. This stimulating action is not impaired in the h.p.p. muscle
The Static and Dynamic Lattice Changes Induced by Hydrogen Adsorption on NiAl(110)
Static and dynamic changes induced by adsorption of atomic hydrogen on the
NiAl(110) lattice at 130 K have been examined as a function of adsorbate
coverage. Adsorbed hydrogen exists in three distinct phases. At low coverages
the hydrogen is itinerant because of quantum tunneling between sites and
exhibits no observable vibrational modes. Between 0.4 ML and 0.6 ML, substrate
mediated interactions produce an ordered superstructure with c(2x2) symmetry,
and at higher coverages, hydrogen exists as a disordered lattice gas. This
picture of how hydrogen interacts with NiAl(110) is developed from our data and
compared to current theoretical predictions.Comment: 36 pages, including 12 figures, 2 tables and 58 reference
Self-assembly of Microcapsules via Colloidal Bond Hybridization and Anisotropy
Particles with directional interactions are promising building blocks for new
functional materials and may serve as models for biological structures.
Mutually attractive nanoparticles that are deformable due to flexible surface
groups, for example, may spontaneously order themselves into strings, sheets
and large vesicles. Furthermore, anisotropic colloids with attractive patches
can self-assemble into open lattices and colloidal equivalents of molecules and
micelles. However, model systems that combine mutual attraction, anisotropy,
and deformability have---to the best of our knowledge---not been realized.
Here, we synthesize colloidal particles that combine these three
characteristics and obtain self-assembled microcapsules. We propose that mutual
attraction and deformability induce directional interactions via colloidal bond
hybridization. Our particles contain both mutually attractive and repulsive
surface groups that are flexible. Analogous to the simplest chemical bond,
where two isotropic orbitals hybridize into the molecular orbital of H2, these
flexible groups redistribute upon binding. Via colloidal bond hybridization,
isotropic spheres self-assemble into planar monolayers, while anisotropic
snowman-like particles self-assemble into hollow monolayer microcapsules. A
modest change of the building blocks thus results in a significant leap in the
complexity of the self-assembled structures. In other words, these relatively
simple building blocks self-assemble into dramatically more complex structures
than similar particles that are isotropic or non-deformable
Unbiased Metagenomic Sequencing for Pediatric Meningitis in Bangladesh Reveals Neuroinvasive Chikungunya Virus Outbreak and Other Unrealized Pathogens.
The burden of meningitis in low-and-middle-income countries remains significant, but the infectious causes remain largely unknown, impeding institution of evidence-based treatment and prevention decisions. We conducted a validation and application study of unbiased metagenomic next-generation sequencing (mNGS) to elucidate etiologies of meningitis in Bangladesh. This RNA mNGS study was performed on cerebrospinal fluid (CSF) specimens from patients admitted in the largest pediatric hospital, a World Health Organization sentinel site, with known neurologic infections (n = 36), with idiopathic meningitis (n = 25), and with no infection (n = 30), and six environmental samples, collected between 2012 and 2018. We used the IDseq bioinformatics pipeline and machine learning to identify potentially pathogenic microbes, which we then confirmed orthogonally and followed up through phone/home visits. In samples with known etiology and without infections, there was 83% concordance between mNGS and conventional testing. In idiopathic cases, mNGS identified a potential bacterial or viral etiology in 40%. There were three instances of neuroinvasive Chikungunya virus (CHIKV), whose genomes were >99% identical to each other and to a Bangladeshi strain only previously recognized to cause febrile illness in 2017. CHIKV-specific qPCR of all remaining stored CSF samples from children who presented with idiopathic meningitis in 2017 (n = 472) revealed 17 additional CHIKV meningitis cases, exposing an unrecognized meningitis outbreak. Orthogonal molecular confirmation, case-based clinical data, and patient follow-up substantiated the findings. Case-control CSF mNGS surveys can complement conventional diagnostic methods to identify etiologies of meningitis, conduct surveillance, and predict outbreaks. The improved patient- and population-level data can inform evidence-based policy decisions.IMPORTANCE Globally, there are an estimated 10.6 million cases of meningitis and 288,000 deaths every year, with the vast majority occurring in low- and middle-income countries. In addition, many survivors suffer from long-term neurological sequelae. Most laboratories assay only for common bacterial etiologies using culture and directed PCR, and the majority of meningitis cases lack microbiological diagnoses, impeding institution of evidence-based treatment and prevention strategies. We report here the results of a validation and application study of using unbiased metagenomic sequencing to determine etiologies of idiopathic (of unknown cause) cases. This included CSF from patients with known neurologic infections, with idiopathic meningitis, and without infection admitted in the largest children's hospital of Bangladesh and environmental samples. Using mNGS and machine learning, we identified and confirmed an etiology (viral or bacterial) in 40% of idiopathic cases. We detected three instances of Chikungunya virus (CHIKV) that were >99% identical to each other and to a strain previously recognized to cause systemic illness only in 2017. CHIKV qPCR of all remaining stored 472 CSF samples from children who presented with idiopathic meningitis in 2017 at the same hospital uncovered an unrecognized CHIKV meningitis outbreak. CSF mNGS can complement conventional diagnostic methods to identify etiologies of meningitis, and the improved patient- and population-level data can inform better policy decisions
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