Mean Field Theory of the Morphology Transition in Stochastic Diffusion Limited Growth

We propose a mean-field model for describing the averaged properties of a class of stochastic diffusion-limited growth systems. We then show that this model exhibits a morphology transition from a dense-branching structure with a convex envelope to a dendritic one with an overall concave morphology. We have also constructed an order parameter which describes the transition quantitatively. The transition is shown to be continuous, which can be verified by noting the non-existence of any hysteresis.Comment: 16 pages, 5 figure

Energy Calibration of b-Quark Jets with Z->b-bbar Decays at the Tevatron Collider

The energy measurement of jets produced by b-quarks at hadron colliders suffers from biases due to the peculiarities of the hadronization and decay of the originating B hadron. The impact of these effects can be estimated by reconstructing the mass of Z boson decays into pairs of b-quark jets. From a sample of 584 pb-1 of data collected by the CDF experiment in 1.96 TeV proton-antiproton collisions at the Tevatron collider, we show how the Z signal can be identified and measured. Using the reconstructed mass of Z candidates we determine a jet energy scale factor for b-quark jets with a precision better than 2%. This measurement allows a reduction of one of the dominant source of uncertainty in analyses based on high transverse momentum b-quark jets. We also determine, as a cross-check of our analysis, the Z boson cross section in hadronic collisions using the b-bbar final state as sigma x B(Z->b-bbar) = 1578 +636 -410 pb.Comment: 35 pages, 9 figures, submitted to Nuclear Instruments and Methods in Physics Research Section

Front Stability in Mean Field Models of Diffusion Limited Growth

We present calculations of the stability of planar fronts in two mean field models of diffusion limited growth. The steady state solution for the front can exist for a continuous family of velocities, we show that the selected velocity is given by marginal stability theory. We find that naive mean field theory has no instability to transverse perturbations, while a threshold mean field theory has such a Mullins-Sekerka instability. These results place on firm theoretical ground the observed lack of the dendritic morphology in naive mean field theory and its presence in threshold models. The existence of a Mullins-Sekerka instability is related to the behavior of the mean field theories in the zero-undercooling limit.Comment: 26 pp. revtex, 7 uuencoded ps figures. submitted to PR

Promoting Adult Resilience in the Workplace: Synthesizing Mental Health and Work-Life Balance Approaches

Mental health in the workplace is a major concern, with rising rates of depression and stress impacting productivity and well-being. Resilient adults are adaptable and able to manage their working and personal lives, as well as the demands of the workplace and technological change. The pilot for an innovative, prevention program, the Promoting Adult Resilience (PAR) program, was conducted in a resource-sector company over 11 weeks with 21 employees taking part and a comparison group drawn from a parallel study on adult well-being. The sessions synthesised cognitive behavioural and mental health promotion strategies with work-life balance to promote mental health well-being amongst working adults. Participant outcomes and intervention integrity were assessed through the duration of the program. Process evaluation assessed the manualised program, the facilitator, the volunteers as participants and diary notes from the facilitator on each session, and found that intervention integrity was maintained throughout the program. Pre and post testing of the participants of the PAR program showed significantly reduced levels of depression and stress, increased satisfaction with balancing work and personal lives and improved levels of coping self-efficacy, in relation to the comparison group

Accessing Sexual and Reproductive Health Information and Services: A Mixed Methods Study of Young Women’s Needs and Experiences in Soweto, South Africa

Young women and girls in South Africa are at high risk of unintended pregnancy and HIV. Previous studies have reported barriers to contraceptive and other sexual and reproductive health (SRH) services among young women in this context. We aimed to assess young women’s SRH knowledge and experiences and to determine how they get SRH information and services in Soweto, South Africa using quantitative and qualitative methods. Young women, aged 18-24, recruited from primary health clinics and a shopping mall, reported that they have access to SRH information and know where to obtain services. However there are challenges to accessing and utilizing information and services including providers’ unsupportive attitudes, uneven power dynamics in relationships and communication issues with parents and community members. There is a need to assist young women in understanding the significance of SRH information. They need access to age-appropriate, youth-friendly services in order to have healthy sexual experiences. Keywords: HIV, gender-based violence, contraception, abortio

Aggregation Patterns in Stressed Bacteria

We study the formation of spot patterns seen in a variety of bacterial species when the bacteria are subjected to oxidative stress due to hazardous byproducts of respiration. Our approach consists of coupling the cell density field to a chemoattractant concentration as well as to nutrient and waste fields. The latter serves as a triggering field for emission of chemoattractant. Important elements in the proposed model include the propagation of a front of motile bacteria radially outward form an initial site, a Turing instability of the uniformly dense state and a reduction of motility for cells sufficiently far behind the front. The wide variety of patterns seen in the experiments is explained as being due the variation of the details of the initiation of the chemoattractant emission as well as the transition to a non-motile phase.Comment: 4 pages, REVTeX with 4 postscript figures (uuencoded) Figures 1a and 1b are available from the authors; paper submitted to PRL

Novel type of phase transition in a system of self-driven particles

A simple model with a novel type of dynamics is introduced in order to investigate the emergence of self-ordered motion in systems of particles with biologically motivated interaction. In our model particles are driven with a constant absolute velocity and at each time step assume the average direction of motion of the particles in their neighborhood with some random perturbation ($\eta$) added. We present numerical evidence that this model results in a kinetic phase transition from no transport (zero average velocity, $| {\bf v}_a | =0$) to finite net transport through spontaneous symmetry breaking of the rotational symmetry. The transition is continuous since $| {\bf v}_a |$ is found to scale as $(\eta_c-\eta)^\beta$ with $\beta\simeq 0.45$

The new anti-actin agent dihydrohalichondramide reveals fenestrae-forming centers in hepatic endothelial cells

BACKGROUND: Liver sinusoidal endothelial cells (LSECs) react to different anti-actin agents by increasing their number of fenestrae. A new structure related to fenestrae formation could be observed when LSECs were treated with misakinolide. In this study, we investigated the effects of two new actin-binding agents on fenestrae dynamics. High-resolution microscopy, including immunocytochemistry and a combination of fluorescence- and scanning electron microscopy was applied. RESULTS: Halichondramide and dihydrohalichondramide disrupt microfilaments within 10 minutes and double the number of fenestrae in 30 minutes. Dihydrohalichondramide induces fenestrae-forming centers, whereas halichondramide only revealed fenestrae-forming centers without attached rows of fenestrae with increasing diameter. Correlative microscopy showed the absence of actin filaments (F-actin) in sieve plates and fenestrae-forming centers. Comparable experiments on umbilical vein endothelial cells and bone marrow sinusoidal endothelial cells revealed cell contraction without the appearance of fenestrae or fenestrae-forming centers. CONCLUSION: (I) A comparison of all anti-actin agents tested so far, revealed that the only activity that misakinolide and dihydrohalichondramide have in common is their barbed end capping activity; (II) this activity seems to slow down the process of fenestrae formation to such extent that it becomes possible to resolve fenestrae-forming centers; (III) fenestrae formation resulting from microfilament disruption is probably unique to LSECs

Development of FTK architecture: a fast hardware track trigger for the ATLAS detector

The Fast Tracker (FTK) is a proposed upgrade to the ATLAS trigger system that will operate at full Level-1 output rates and provide high quality tracks reconstructed over the entire detector by the start of processing in Level-2. FTK solves the combinatorial challenge inherent to tracking by exploiting the massive parallelism of Associative Memories (AM) that can compare inner detector hits to millions of pre-calculated patterns simultaneously. The tracking problem within matched patterns is further simplified by using pre-computed linearized fitting constants and leveraging fast DSP's in modern commercial FPGA's. Overall, FTK is able to compute the helix parameters for all tracks in an event and apply quality cuts in approximately one millisecond. By employing a pipelined architecture, FTK is able to continuously operate at Level-1 rates without deadtime. The system design is defined and studied using ATLAS full simulation. Reconstruction quality is evaluated for single muon events with zero pileup, as well as WH events at the LHC design luminosity. FTK results are compared with the tracking capability of an offline algorithm.Comment: To be published in the proceedings of DPF-2009, Detroit, MI, July 2009, eConf C09072

The Evolution of FTK, a Real-Time Tracker for Hadron Collider Experiments

We describe the architecture evolution of the highly-parallel dedicated processor FTK, which is driven by the simulation of LHC events at high luminosity (1034 cm-2 s-1). FTK is able to provide precise on-line track reconstruction for future hadronic collider experiments. The processor, organized in a two-tiered pipelined architecture, execute very fast algorithms based on the use of a large bank of pre-stored patterns of trajectory points (first tier) in combination with full resolution track fitting to refine pattern recognition and to determine off-line quality track parameters. We describe here how the high luminosity simulation results have produced a new organization of the hardware inside the FTK processor core.Comment: 11th ICATPP conferenc