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 $l=1$, the quadrupole and higher spin deformations ($l\geq 2$) 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 $G$ and $\Lambda$ is governed by a RG equation together with an appropriate identification of RG scales with points in spacetime. The dynamics of the fields $G$ and $\Lambda$ 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, $G$ and $\Lambda$ carry energy and momentum. It is tested in the setting of homogeneous-isotropic cosmology and is compared to alternative approaches where the fields $G$ and $\Lambda$ 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