Computing the local pressure in molecular dynamics simulations

Computer simulations of inhomogeneous soft matter systems often require accurate methods for computing the local pressure. We present a simple derivation, based on the virial relation, of two equivalent expressions for the local (atomistic) pressure in a molecular dynamics simulation. One of these expressions, previously derived by other authors via a different route, involves summation over interactions between particles within the region of interest; the other involves summation over interactions across the boundary of the region of interest. We illustrate our derivation using simulations of a simple osmotic system; both expressions produce accurate results even when the region of interest over which the pressure is measured is very small.Comment: 11 pages, 4 figure

Tactical Themes for Rangeland Research

The problems threatening the conservation and management of rangeland, over one-half of the world’s terrestrial surfaces, are significant and growing. Current assessments of drivers and externalities shaping these problems have resulted in strategies intended to result in sustainable development of these lands and their resources. However, how can individual scientists and individual research programs support the needed strategies and goals? What can we realistically contribute and accomplish? We believe that technology can connect individual scientists and their science to the problems manifest in rangelands over the world, in a more rapid exchange than has occurred in the past. Recognition of local challenges, innovations, and scientific tests of the effectiveness of our technological solutions to these problems can keep pace with rapid change and help us adapt to that change. However, to do this, we have to invest in a process of connecting science to landscapes. Our tactics are to link, openly and collaboratively, the scientific method to discrete, specific, managed landscapes. We term these collective tactics, our fundamental research theme, “Landscape Portals”. All of the elements of this theme exist currently, to various degrees, but they lack cohesion and interactive, real-time connections. Future investment requires two basic, tactical scientific behaviors: a post-normal application of science in support of land management by hypothesis and a scientific method modified to accommodate a data intensive scientific inquiry directed towards adaptive management. These behaviors support our “Landscape Portals” theme: science conducted in a highly interactive, transparent, data enriched, locally relevant, globally connected, popularly translated, and ecologically robust manner

AWAT3.0 - Präzise Bestimmung von Niederschlags- und Verdunstungsereignissen aus Lysimetermessungen mit Hilfe eines verbesserten Datenfilters

Eine genaue Quantifizierung von Evapotranspirations- (ET) und Niederschlagsraten (P) ist für viele Fragen hinsichtlich des Wasser-, Stoff- und Energiehaushalts im System Boden-Pflanze-Atmosphäre von großer Bedeutung. Moderne wägbare Lysimeter mit hoher zeitlicher Auflösung der Gewichtsmessung bieten die präziseste Information für ET und P. Dabei wird ein Ansteigen der Gesamtmasse als P und ein Abfallen als ET interpretiert. Eine Schwierigkeit bei dieser Interpretation ergibt sich daraus, dass die realen Signale durch Messrauschen (z.B. durch Wind) überlagert werden. Wirkliche Signale können in zwei Schritten von Rauschen getrennt werden: (i) Glättung der Daten (z.B. gleitender Mittelwert) mit einem bestimmten Mittelungsfenster und (ii) Einführung eines Schwellenwertes, als Maß für die Messungenauigkeit, der signifikante von nicht signifikanten Masseänderungen trennt. In den letzten Jahren wurden einige Probleme hinsichtlich dieser Vorgehensweise identifiziert und gelöst. Dazu gehören die adaptive Fensterbreite für die Mittelung und der adaptive Schwellenwert für die Trennung von signifikanten von nicht signifikanten Änderungen (Adaptive Window and Adaptive Threshold - AWAT) und eine Interpolation der so gewonnenen Daten, um stufenförmige Änderungen nach der Schwellenwertberechnung zu vermeiden. Ein bisher nicht gelöstes Problem war die systematische Unterschätzung der Flüsse bei jedem Wechsel in der Fließrichtung (von P zu ET oder ET zu P) als Folge der Schwellenwertberechnung. In diesem Beitrag analysieren wir diesen Fehler und schlagen eine heuristische Lösung, die sogenannte „Snap-Routine“, vor. Anhand von synthetischen Daten wird diese Routine kalibriert und getestet. Anschließend wird sie an realen Daten eines „TERENO-Lysimeters“ angewendet. Der systematische Fehler ist unabhängig von der Quantität eines Ereignisses und damit wird der relative Fehler umso größer je kleiner das Ereignis ist. Bei Tau- oder Reifereignissen kann der Fehler dieselbe Größenordnung wie der Fluss haben. Mit der „Snap-Routine“ wird dieser Fehler effektiv behoben, so dass eine Wiedergabe der Flüsse fast ohne systematischen Effekt möglich ist

Spatial Light Modulators for the Manipulation of Individual Atoms

We propose a novel dipole trapping scheme using spatial light modulators (SLM) for the manipulation of individual atoms. The scheme uses a high numerical aperture microscope to map the intensity distribution of a SLM onto a cloud of cold atoms. The regions of high intensity act as optical dipole force traps. With a SLM fast enough to modify the trapping potential in real time, this technique is well suited for the controlled addressing and manipulation of arbitrarily selected atoms.Comment: 9 pages, 5 figure

Power Spectrum Analysis of Physikalisch-Technische Bundesanstalt Decay-Rate Data: Evidence for Solar Rotational Modulation

Evidence for an anomalous annual periodicity in certain nuclear decay data has led to speculation concerning a possible solar influence on nuclear processes. We have recently analyzed data concerning the decay rates of Cl-36 and Si-32, acquired at the Brookhaven National Laboratory (BNL), to search for evidence that might be indicative of a process involving solar rotation. Smoothing of the power spectrum by weighted-running-mean analysis leads to a significant peak at frequency 11.18/yr, which is lower than the equatorial synodic rotation rates of the convection and radiative zones. This article concerns measurements of the decay rates of Ra-226 acquired at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. We find that a similar (but not identical) analysis yields a significant peak in the PTB dataset at frequency 11.21/yr, and a peak in the BNL dataset at 11.25/yr. The change in the BNL result is not significant since the uncertainties in the BNL and PTB analyses are estimated to be 0.13/yr and 0.07/yr, respectively. Combining the two running means by forming the joint power statistic leads to a highly significant peak at frequency 11.23/yr. We comment briefly on the possible implications of these results for solar physics and for particle physics.Comment: 15 pages, 13 figure

A Nanofiber-Based Optical Conveyor Belt for Cold Atoms

We demonstrate optical transport of cold cesium atoms over millimeter-scale distances along an optical nanofiber. The atoms are trapped in a one-dimensional optical lattice formed by a two-color evanescent field surrounding the nanofiber, far red- and blue-detuned with respect to the atomic transition. The blue-detuned field is a propagating nanofiber-guided mode while the red-detuned field is a standing-wave mode which leads to the periodic axial confinement of the atoms. Here, this standing wave is used for transporting the atoms along the nanofiber by mutually detuning the two counter-propagating fields which form the standing wave. The performance and limitations of the nanofiber-based transport are evaluated and possible applications are discussed

Search for Flavoured Multiquarks in a Simple Bag Model

We use a bag model to study flavoured mesonic $(Qq\bar q\bar q)$ and baryonic $({\overline Q}qqqq)$ states, where one heavy quark $Q$ is associated with light quarks or antiquarks, and search for possible stable multiquarks. No bound state is found. However some states lie not too high above their dissociation threshold, suggesting the possibility of resonances, or perhaps bound states in improved models.Comment: REVTEX, VERSION 3.

Control of oocyte release by progesterone receptor-regulated gene expression

The progesterone receptor (PGR) is a nuclear receptor transcription factor that is essential for female fertility, in part due to its control of oocyte release from the ovary, or ovulation. In all mammals studied to date, ovarian expression of PGR is restricted primarily to granulosa cells of follicles destined to ovulate. Granulosa cell expression of PGR is induced by the pituitary Luteinizing Hormone (LH) surge via mechanisms that are not entirely understood, but which involve activation of Protein Kinase A and modification of Sp1/Sp3 transcription factors on the PGR promoter. Null mutations for PGR or treatment with PGR antagonists block ovulation in all species analyzed, including humans. The cellular mechanisms by which PGR regulates ovulation are currently under investigation, with several downstream pathways having been identified as PGR-regulated and potentially involved in follicular rupture. Interestingly, none of these PGR-regulated genes has been demonstrated to be a direct transcriptional target of PGR. Rather, in ovarian granulosa cells, PGR may act as an inducible coregulator for constitutively bound Sp1/Sp3 transcription factors, which are key regulators for a discrete cohort of ovulatory genes