Using White Dish CMB Anisotropy Data to Probe Open and Flat-Lambda CDM Cosmogonies

We use data from the White Dish experiment to set limits on cosmic microwave background radiation anisotropies in open and spatially-flat-Lambda cold dark matter cosmogonies. We account for the White Dish calibration uncertainty, and marginalize over the offset and gradient removed from the data. Our 2-sigma upper limits are larger than those derived previously. These upper limits are consistent with those derived from the $COBE$-DMR data for all models tested.Comment: 17 pages of latex. Uses aasms4.sty. 4 figures included. Submitted to ApJ

Local u'g'r'i'z' Standard Stars in the Chandra Deep Field-South

Because several observing programs are underway in various spectral regimes to explore the Chandra Deep Field South (CDF-S), the value of local photometric standards is obvious. As part of an NOAO Surveys Program to establish u'g'r'i'z' standard stars in the southern hemisphere, we have observed the central region of the CDF-S to create local standards for use by other investigators using these filters. As a courtesy, we present the CDF-S standards to the public now, although the main program will not finish until mid-2005.Comment: Accepted by AJ (scheduled for October 2003 issue). 26 pages, 5 tables, 5 figures. High resolution version of Figure 7 available at http://home.fnal.gov/~dtucker/Southern_ugriz/index.htm

Vascular signalling mediated by ZWILLE potentiates WUSCHEL function during shoot meristem stem cell development in the Arabidopsis embryo

Stem cells are maintained in an undifferentiated state by signals from their microenvironment, the stem cell niche. Despite its central role for organogenesis throughout the plant's life, little is known about how niche development is regulated in the Arabidopsis embryo. Here we show that, in the absence of functional ZWILLE (ZLL), which is a member of the ARGONAUTE (AGO) family, stem cell-specific expression of the signal peptide gene CLAVATA3 (CLV3) is not maintained despite increased levels of the homeodomain transcription factor WUSCHEL (WUS), which is expressed in the organising centre (OC) of the niche and normally promotes stem cell identity. Tissue-specific expression indicates that ZLL acts to maintain the stem cells from the neighbouring vascular primordium, providing direct evidence for a non-cell-autonomous mechanism. Furthermore, mutant and marker gene analyses suggest that during shoot meristem formation, ZLL functions in a similar manner but in a sequential order with its close homologue AGO1, which mediates RNA interference. Thus, WUS-dependent OC signalling to the stem cells is promoted by AGO1 and subsequently maintained by a provascular ZLL-dependent signalling pathway.Matthew R. Tucker, Annika Hinze, Elise J. Tucker, Shinobu Takada, Gerd Jürgens and Thomas Lau

Perceived Community Cohesion and the Stress Process in Youth

Using survey data from two youth samples, one rural and one urban, we examine the role and significance of perceived community cohesion in the stress process. In particular, we assess the extent to which community attachment and detachment are related to depressed mood, problem substance use, and delinquency net of social statuses, stress exposure, and personal attributes. In addition, we explore the degree to which those dimensions of community cohesion explain or condition the links between the above stress-process components (e.g., social statuses, stress exposure, and personal attributes) and well-being. We find remarkably similar results across samples: community attachment is related to lower odds of problem substance use and delinquency; community detachment is related to higher levels of depressed mood, problem substance use, and delinquency; and community attachment buffers the link between stress and problem substance use. With respect to depressed mood, however, the rural youth show greater vulnerability to stress than the urban youth and unique benefits from community attachment compared to the latter. Our findings highlight the roles of community attachment and detachment in the stress process and underscore the importance of each for youth well-being in rural and urban settings

Magnetic structure of Ba(TiO)Cu4_4(PO4_4)4_4 probed using spherical neutron polarimetry

The antiferromagnetic compound Ba(TiO)Cu$_4$(PO$_4$)$_4$ contains square cupola of corner-sharing CuO$_4$ plaquettes, which were proposed to form effective quadrupolar order. To identify the magnetic structure, we have performed spherical neutron polarimetry measurements. Based on symmetry analysis and careful measurements we conclude that the orientation of the Cu$^{2+}$ spins form a non-collinear in-out structure with spins approximately perpendicular to the CuO$_4$ motif. Strong Dzyaloshinskii-Moriya interaction naturally lends itself to explain this phenomenon. The identification of the ground state magnetic structure should serve well for future theoretical and experimental studies into this and closely related compounds.Comment: 9 pages, 4 figure

The Transition State in a Noisy Environment

Transition State Theory overestimates reaction rates in solution because conventional dividing surfaces between reagents and products are crossed many times by the same reactive trajectory. We describe a recipe for constructing a time-dependent dividing surface free of such recrossings in the presence of noise. The no-recrossing limit of Transition State Theory thus becomes generally available for the description of reactions in a fluctuating environment

On the Energy-Momentum Density of Gravitational Plane Waves

By embedding Einstein's original formulation of GR into a broader context we show that a dynamic covariant description of gravitational stress-energy emerges naturally from a variational principle. A tensor $T^G$ is constructed from a contraction of the Bel tensor with a symmetric covariant second degree tensor field $\Phi$ and has a form analogous to the stress-energy tensor of the Maxwell field in an arbitrary space-time. For plane-fronted gravitational waves helicity-2 polarised (graviton) states can be identified carrying non-zero energy and momentum.Comment: 10 pages, no figure

Aspects of quantum energy and stress in inhomogeneous unbounded dielectric continua

This article explores a number of issues associated with the problem of calculating and detecting electromagnetic quantum induced energy and stress in a stationary dielectric material with a smooth inhomogeneous polarizability. By concentrating on a particular system composed of an ENZ-type (epsilon-near-zero) meta-material, chosen to have a particular anisotropic and smooth inhomogeneous permittivity, confined in an infinitely long perfectly conducting open rectangular waveguide, we are able to deduce analytically from the source-free Maxwell’s equations and their boundary conditions a complete set of bounded harmonic electromagnetic evanescent eigen-modes and their associated eigen-frequencies. Since these solutions prohibit the existence of asymptotic scattering states in the guide, the application of the conventional Lifshitz approach to the Casimir stress problem becomes uncertain. An alternative approach is adopted based upon the spectral properties of the system and a regularization scheme constructed with direct applicability to more general systems composed of dielectrics with smooth inhomogeneous permittivities and open systems that may only admit evanescent modes. This more general scheme enables one, for the first time, to prescribe precise criteria for the extraction of finite quantum expectation values from regularized mode sums together with error bounds on these values, and is used to derive analytic or numeric results for regularized electromagnetic ground state expectation values in the guide