Second Order Correlation Function of a Phase Fluctuating Bose-Einstein Condensate

The coherence properties of phase fluctuating Bose-Einstein condensates are studied both theoretically and experimentally. We derive a general expression for the N-particle correlation function of a condensed Bose gas in a highly elongated trapping potential. The second order correlation function is analyzed in detail and an interferometric method to directly measure it is discussed and experimentally implemented. Using a Bragg diffraction interferometer, we measure intensity correlations in the interference pattern generated by two spatially displaced copies of a parent condensate. Our experiment demonstrates how to characterize the second order correlation function of a highly elongated condensate and to measure its phase coherence length.Comment: 22 pages, 5 figure

Characterization and control of phase fluctuations in elongated Bose-Einstein condensates

Quasi one dimensional Bose-Einstein condensates (BECs) in elongated traps exhibit significant phase fluctuations even at very low temperatures. We present recent experimental results on the dynamic transformation of phase fluctuations into density modulations during time-of-flight and show the excellent quantitative agreement with the theoretical prediction. In addition we confirm that under our experimental conditions, in the magnetic trap density modulations are strongly suppressed even when the phase fluctuates. The paper also discusses our theoretical results on control of the condensate phase by employing a time-dependent perturbation. Our results set important limitations on future applications of BEC in precision atom interferometry and atom optics, but at the same time suggest pathways to overcome these limitations.Comment: 9 pages, 7 figure

Perturbation theory for anisotropic dielectric interfaces, and application to sub-pixel smoothing of discretized numerical methods

We derive a correct first-order perturbation theory in electromagnetism for cases where an interface between two anisotropic dielectric materials is slightly shifted. Most previous perturbative methods give incorrect results for this case, even to lowest order, because of the complicated discontinuous boundary conditions on the electric field at such an interface. Our final expression is simply a surface integral, over the material interface, of the continuous field components from the unperturbed structure. The derivation is based on a "localized" coordinate-transformation technique, which avoids both the problem of field discontinuities and the challenge of constructing an explicit coordinate transformation by taking a limit in which a coordinate perturbation is infinitesimally localized around the boundary. Not only is our result potentially useful in evaluating boundary perturbations, e.g. from fabrication imperfections, in highly anisotropic media such as many metamaterials, but it also has a direct application in numerical electromagnetism. In particular, we show how it leads to a sub-pixel smoothing scheme to ameliorate staircasing effects in discretized simulations of anisotropic media, in such a way as to greatly reduce the numerical errors compared to other proposed smoothing schemes.Comment: 10 page

Contraception for Adolescents During the Coronavirus Disease 2019 Pandemic

Our recent publication, Providing Contraception for Young People During a Pandemic is Essential Healthcare, was written in response to the sudden shift towards low-contact or no-contact medicine in the wake of the COVID-19 pandemic. Ensuring access to contraception is essential as every 6 months of lockdown can result in 47 million women losing access to contraception, resulting in an additional 7 million of unintended pregnancies. We welcome the letters submitted by Alouini/Venslauskaite and Uzoigwe/Ali as they exemplify common misperceptions within the medical community about contraception. The question of whether a physical exam is required prior to a contraception prescription, the safety of emergency contraception, and abstinence counseling are addressed below

Left ventricular echocardiographic and histologic changes: Impact of chronic unloading by an implantable ventricular assist device

AbstractObjectives. We studied the effects of chronic left ventricular unloading by a ventricular assist device and assessed left ventricular morphologic and histologic changes.Background. The implantable left ventricular assist device has been effective as a “bridge” to cardiac transplantation. Although there are reports documenting its circulatory support, little is known about the effects of chronic left ventricular unloading on the heart itself.Methods. We performed intraoperative transesophageal echocardiography at the insertion and explantation of a HeartMate left ventricular assist device in 19 patients with end-stage heart failure. They were supported by the assist device for 3 to 153 days (mean [±SD] 68±33). Measurements were taken retrospectively to obtain left atrial and ventricular diameters and interventricular septal and posterior wall thicknesses. Histologic examinations were made from the left ventricular myocardial specimens of 15 patients at the times of insertion and explantation for heart transplantation. Insertion and explantation specimens were compared qualitatively (0 to 3 scale) for wavy fibers, contraction band necrosis and fibrosis, with quantitative measurement of minimal myocyte diameter across the nucleus.Results. Left atrial and left ventricular diastolic and systolic diameters decreased immediately after insertion of the left ventricular assist device (from 46 to 35, 63 to 41 and 59 to 36 mm, respectively, all p < 0.001). Left ventricular wall thickness increased from 10 to 14 mm (p < 0.001) for the interventricular septum and from 10 to 13 mm for the posterior wall (p < 0.001). No echocardiographic measurements showed significant subsequent changes at the chronic stage. Myocardial histologic findings demonstrated a reduction in myocyte damage (from 1.9 to 0.5, p < 0.001, for wavy fiber and from 1.3 to 0.2, p < 0.01, for contraction band necrosis) and an increase in fibrosis (from 1.3 to 1.9, p < 0.05), but without significant change in myocyte diameter (from 15.6 to 16.8 μm, p = 0.065).Conclusions.Left ventricular unloading with the implantable assist device induces an immediate increase in wall thickness, consistent with the reduction in chamber size, thereby decreasing wall stress. Chronic unloading allows myocardial healing and fibrosis without evidence for ongoing myocyte damage or atrophy. Left ventricular assist device insertion may have a role in “resting” the ventricle for selected patients with heart failure

Cellular levels of p120 catenin function as a set point for cadherin expression levels in microvascular endothelial cells

The mechanisms by which catenins regulate cadherin function are not fully understood, and the precise function of p120 catenin (p120ctn) has remained particularly elusive. In microvascular endothelial cells, p120ctn colocalized extensively with cell surface VE-cadherin, but failed to colocalize with VE-cadherin that had entered intracellular degradative compartments. To test the possibility that p120ctn binding to VE-cadherin regulates VE-cadherin internalization, a series of approaches were undertaken to manipulate p120ctn availability to endogenous VE-cadherin. Expression of VE-cadherin mutants that competed for p120ctn binding triggered the degradation of endogenous VE-cadherin. Similarly, reducing levels of p120ctn using siRNA caused a dramatic and dose-related reduction in cellular levels of VE-cadherin. In contrast, overexpression of p120ctn increased VE-cadherin cell surface levels and inhibited entry of cell surface VE-cadherin into degradative compartments. These results demonstrate that cellular levels of p120ctn function as a set point mechanism that regulates cadherin expression levels, and that a major function of p120ctn is to control cadherin internalization and degradation

Testing for hereditary thrombophilia: a retrospective analysis of testing referred to a national laboratory

<p>Abstract</p> <p>Background</p> <p>Predisposition to venous thrombosis may be assessed through testing for defects and/or deficiencies of a number of hereditary factors. There is potential for confusion about which of these tests are appropriate in which settings. At least one set of recommendations has been published to guide such testing, but it is unclear how widely these have been disseminated.</p> <p>Methods</p> <p>We performed a retrospective analysis of laboratory orders and results at a national referral laboratory to gain insight into physicians' ordering practices, specifically comparing them against the ordering practices recommended by a 2002 College of American Pathologists (CAP) consensus conference on thrombophilia testing. Measurements included absolute and relative ordering volumes and positivity rates from approximately 200,000 thrombophilia tests performed from September 2005 through August 2006 at a national reference laboratory. Quality control data were used to estimate the proportion of samples that may have been affected by anticoagulant therapy. A sample of ordering laboratories was surveyed in order to assess potential measurement bias.</p> <p>Results</p> <p>Total antigen assays for protein C, protein S and antithrombin were ordered almost as frequently as functional assays for these analytes. The DNA test for factor V Leiden was ordered much more often than the corresponding functional assay. In addition, relative positivity rates coupled with elevations in prothrombin time (PT) in many of these patients suggest that these tests are often ordered in the setting of oral anticoagulant therapy.</p> <p>Conclusion</p> <p>In this real-world setting, testing for inherited thrombophilia is frequently at odds with the recommendations of the CAP consensus conference. There is a need for wider dissemination of concise thrombophilia testing guidelines.</p