1,494 research outputs found
Nkx6.1 is essential for maintaining the functional state of pancreatic beta cells
Recently, loss of beta-cell-specific traits has been proposed as an early cause of beta cell failure in diabetes. However, the molecular mechanisms that underlie the loss of beta cell features remain unclear. Here, we identify an Nkx6.1-controlled gene regulatory network as essential for maintaining the functional and molecular traits of mature beta cells. Conditional Nkx6.1 inactivation in adult mice caused rapid-onset diabetes and hypoinsulinemia. Genome-wide analysis of Nkx6.1-regulated genes and functional assays further revealed a critical role for Nkx6.1 in the control of insulin biosynthesis, insulin secretion, and beta cell proliferation. Over time, Nkx6.1-deficient beta cells acquired molecular characteristics of delta cells, revealing a molecular link between impaired beta cell functional properties and loss of cell identity. Given that Nkx6.1 levels are reduced in human type 2 diabetic beta cells, our study lends support to the concept that loss of beta cell features could contribute to the pathogenesis of diabetes
Quadrupole Instabilities of Relativistic Rotating Membranes
We generalize recent study of the stability of isotropic (spherical) rotating
membranes to the anisotropic ellipsoidal membrane. We find that while the
stability persists for deformations of spin , the quadrupole and higher
spin deformations () lead to instabilities. We find the relevant
instability modes and the corresponding eigenvalues. These indicate that the
ellipsoidal rotating membranes generically decay into finger-like
configurations.Comment: 5 pages, 1 figur
An observation of spin-valve effects in a semiconductor field effect transistor: a novel spintronic device
We present the first spintronic semiconductor field effect transistor.
The injector and collector contacts of this device were made from magnetic
permalloy thin films with different coercive fields so that they could be
magnetized either parallel or antiparallel to each other in different applied
magnetic fields. The conducting medium was a two dimensional electron gas
(2DEG) formed in an AlSb/InAs quantum well.
Data from this device suggest that its resistance is controlled by two
different types of spin-valve effect: the first occurring at the
ferromagnet-2DEG interfaces; and the second occuring in direct propagation
between contacts.Comment: 4 pages, 2 figure
Performance of an acousto-optic Bragg cell under ion microbeam irradiation
An acousto optic (AO) deflector composed of PbMoO{sub 4} was exposed to 4 MeV protons while operating under Bragg angle conditions. An ion beam in air of 1 mm width was directed normal to the crystal face and laser beam. Between exposures, the approximately 13 mm x 8.5 mm AO deflector was mechanically translated in two dimensions in front of the fixed ion beam. The AO diffraction efficiency was mapped and was observed to change as a function of ion beam location and dose rate. These effects are attributed to the induced change in the temperature distribution of the crystal, which changed the sonic velocity and refractive index. Similar effects were observed when the ion beam was directed at the acoustic transducer
Path lengths in turbulence
By tracking tracer particles at high speeds and for long times, we study the
geometric statistics of Lagrangian trajectories in an intensely turbulent
laboratory flow. In particular, we consider the distinction between the
displacement of particles from their initial positions and the total distance
they travel. The difference of these two quantities shows power-law scaling in
the inertial range. By comparing them with simulations of a chaotic but
non-turbulent flow and a Lagrangian Stochastic model, we suggest that our
results are a signature of turbulence.Comment: accepted for publication in Journal of Statistical Physic
The effect of Covid-19 on pediatric surgical case volume.
Introduction
The COVID-19 pandemic has had an unprecedented ef- fect on hospital systems. Policy changes lead to de- creased hospital visits as well as surgical case volume. The literature on pediatric surgical case volume during the pandemic is sparse. Throughout the country, hospitals sought various policies to preserve personal protective equipment and other hospital resources, and to minimize avoidable peri- and postoperative sequelae due to COVID-19 infection. Our hospital first placed a hold on all elective surgeries. Later, all elective cases required a preoperative negative COVID test prior to proceed- ing. We sought to review the sequelae of our hospital’s policy in response to COVID-19. We identified trends in surgical case volume and cancellations due to a positive COVID-19 test. We also reviewed postoperative out- comes of cases with a positive test.
Material and Methods
This study was approved by the institutional IRB. Data was retrospectively collected on all surgical cases at our children’s hospital between March 2019 and March
2021. We marked the start of the COVID-19 pandemic as March 2020, when elective cases were suspended. A required preoperative negative COVID-19 test was im- plemented in May 2020. We identified pre-operative COVID-19 test results,the posted urgency of each case and 30-day outcomes from medical records.
Results
From March 2019 to March 2021, we identified 25,496 completed surgeries and 3,503 cancellations. 12,024 ca- ses proceeded during the first year of the pandemic, which appeared lower, compared to pre-pandemic case numbers. Of those, 2,785 (23%) cases were considered urgent or emergent. The average number of completed monthly cases fell from a pre-pandemic number of 1,123 to a pandemic number of 925. When comparing to a pre- pandemic month, average monthly case volume declined by 19%, with the largest decline noted to be 66%. There was a monthly average of 189 total cancellations between March 2020 and March 2021. 34 (18%) of those were for a positive preoperative COVID test. A total of 139 sur- geries commenced despite concomitant COVID-19 in- fection. 25 (18 %) had identifiable respiratory symptomsdocumented preoperatively. 13 (9 %) were deemed to have a respiratory complication afterward. Of those, three patients (2%) had a prolonged, and one (1%) had an unexpected reintubation. The remaining nine (6%) pa- tients had a prolonged oxygen requirement.
Conclusion
The COVID pandemic left operating rooms struggling to determine how to safely provide care to patients. This study demonstrated how the policies of one hospital af- fected the operating room case volume and how conco- mitant COVID infection affected outcomes in those that proceeded with surgery
A Conformally Invariant Holographic Two-Point Function on the Berger Sphere
We apply our previous work on Green's functions for the four-dimensional
quaternionic Taub-NUT manifold to obtain a scalar two-point function on the
homogeneously squashed three-sphere (otherwise known as the Berger sphere),
which lies at its conformal infinity. Using basic notions from conformal
geometry and the theory of boundary value problems, in particular the
Dirichlet-to-Robin operator, we establish that our two-point correlation
function is conformally invariant and corresponds to a boundary operator of
conformal dimension one. It is plausible that the methods we use could have
more general applications in an AdS/CFT context.Comment: 1+49 pages, no figures. v2: Several typos correcte
Screened Coulomb interactions in metallic alloys: I. Universal screening in the atomic sphere approximation
We have used the locally self-consistent Green's function (LSGF) method in
supercell calculations to establish the distribution of the net charges
assigned to the atomic spheres of the alloy components in metallic alloys with
different compositions and degrees of order. This allows us to determine the
Madelung potential energy of a random alloy in the single-site mean field
approximation which makes the conventional single-site density-functional-
theory coherent potential approximation (SS-DFT-CPA) method practically
identical to the supercell LSGF method with a single-site local interaction
zone that yields an exact solution of the DFT problem. We demonstrate that the
basic mechanism which governs the charge distribution is the screening of the
net charges of the alloy components that makes the direct Coulomb interactions
short-ranged. In the atomic sphere approximation, this screening appears to be
almost independent of the alloy composition, lattice spacing, and crystal
structure. A formalism which allows a consistent treatment of the screened
Coulomb interactions within the single-site mean-filed approximation is
outlined. We also derive the contribution of the screened Coulomb interactions
to the S2 formalism and the generalized perturbation method.Comment: 28 pages, 8 figure
Renormalization group improved gravitational actions: a Brans-Dicke approach
A new framework for exploiting information about the renormalization group
(RG) behavior of gravity in a dynamical context is discussed. The
Einstein-Hilbert action is RG-improved by replacing Newton's constant and the
cosmological constant by scalar functions in the corresponding Lagrangian
density. The position dependence of and is governed by a RG
equation together with an appropriate identification of RG scales with points
in spacetime. The dynamics of the fields and does not admit a
Lagrangian description in general. Within the Lagrangian formalism for the
gravitational field they have the status of externally prescribed
``background'' fields. The metric satisfies an effective Einstein equation
similar to that of Brans-Dicke theory. Its consistency imposes severe
constraints on allowed backgrounds. In the new RG-framework, and
carry energy and momentum. It is tested in the setting of homogeneous-isotropic
cosmology and is compared to alternative approaches where the fields and
do not carry gravitating 4-momentum. The fixed point regime of the
underlying RG flow is studied in detail.Comment: LaTeX, 72 pages, no figure
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