A random walker on a ratchet

We analyze a model for a walker moving on a ratchet potential. This model is motivated by the properties of transport of motor proteins, like kinesin and myosin. The walker consists of two feet represented as two particles coupled nonlinearly through a bistable potential. In contrast to linear coupling, the bistable potential admits a richer dynamics where the ordering of the particles can alternate during the walking. The transitions between the two stable states on the bistable potential correspond to a walking with alternating particles. We distinguish between two main walking styles: alternating and no alternating, resembling the hand-over-hand and the inchworm walking in motor proteins, respectively. When the equilibrium distance between the two particles divided by the periodicity of the ratchet is an integer, we obtain a maximum for the current, indicating optimal transport.Comment: 10 pages, 5 figure

Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?

The origin of striations aligned along the local magnetic field direction in the translucent envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J=2-1 emission obtained with the 10~m submillimeter telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsible for the striations. For both 12CO and 13CO, spatial variations of the J=2-1 to J=1-0 line ratio are small and are not spatially correlated with the striation locations. A medium comprised of unresolved CO emitting substructures (cells) with a beam area filling factor less than unity at any velocity is required to explain the average line ratios and brightness temperatures. We propose that the striations result from the modulation of velocities and the beam filling factor of the cells as a result of either the Kelvin-Helmholtz instability or magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Both processes are likely common features in molecular clouds that are sub-Alfvenic and may explain low column density, cirrus-like features similarly aligned with the magnetic field observed throughout the interstellar medium in far-infrared surveys of dust emission.Comment: 11 pages, 4 figures. Accepted for publication in MNRA

Depression, anxiety, PTSD and comorbidity in perinatal women in Turkey: A longitudinal population-based study

OBJECTIVE: (a) to assess prevalence of depression, anxiety and post-traumatic stress disorder (PTSD) and their comorbidity among women during the perinatal period (b) to examine course of those disorders from pregnancy to 6 months postpartum (c) to determine the rates of new-onset cases at 4-6 weeks and 6 months postpartum. DESIGN: A longitudinal population-based study in which participants completed psychosocial measures of depression, anxiety and PTSD in pregnancy (n = 950), 4-6 weeks (n = 858) and 6 months (n = 829) after birth. SETTING: A consecutive sample of pregnant women were recruited from three maternity hospitals in three cities of Turkey: Istanbul, Ankara and Izmir. MEASURES: Edinburgh Postnatal Depression Scale (EPDS), Hospital Anxiety and Depression Scale (HADS), and Posttraumatic Diagnostic Scale (PDS) were used to assess depression, anxiety and PTSD, respectively. FINDINGS: Depression and PTSD peaked at 4-6 weeks postpartum and then fell at 6 months postpartum, whereas anxiety followed a gradually declining linear-pattern from pregnancy to 6 months postpartum. The prevalence of depression was 14.6% in pregnancy, 32.6% at 4-6 weeks and 18.5% at 6 months postpartum, respectively. The prevalence of PTSD was 5.8% in pregnancy, 11.9% at 4-6 weeks postpartum and 9.2% at 6 months postpartum. Anxiety was highest in pregnancy (29.6%) and then decreased to 24.6% 4-6 weeks after birth and to 16.2% 6 months after birth. New-onset cases were most apparent at 4-6 weeks postpartum: 24.6% for depression; 13.7% for anxiety and 8.9% for PTSD. KEY CONCLUSIONS: A relatively high prevalence of psychological disorders was identified during the perinatal period. Anxiety was most prevalent in pregnancy, and depression and PTSD were highest at 4-6 weeks postpartum. Depression was more common than anxiety 4-6 weeks and 6 months after birth and highly comorbid with anxiety throughout this period. New-onset cases were observed at both 4-6 weeks and 6 months postpartum. IMPLICATIONS: High rates of affective disorders in pregnancy and after birth highlight three main points: first, it is important to have effective perinatal screening to identify women with psychological needs; second, providing early treatment to women experiencing severe psychological problems is essential to ensure psychological well-being of those women and to prevent chronicity; and finally, psychosocial screening and interventions should be offered until at least 6 months after birth to catch new-onset cases

Screening for birth-related PTSD: psychometric properties of the Turkish version of the Posttraumatic Diagnostic Scale in postpartum women in Turkey

Background: Evidence suggests that 4% of women develop posttraumatic stress disorder (PTSD) after childbirth, with a potentially negative impact on women and families. Detection of postpartum PTSD is essential but few measures have been validated in this population. Objective: This study aimed to examine psychometric properties of the Turkish version of the Posttraumatic Diagnostic Scale (PDS) to screen for birth-related PTSD among postpartum women and identify factorial structure of PTSD after birth. Method: PDS was administered to 829 postpartum women recruited from three maternity hospitals in Turkey. Participants with PTSD (N = 68) and a randomly selected group of women without PTSD (N = 66), underwent a structured clinical interview (SCID). Results: PDS demonstrated high internal consistency (α = .89) and test-retest reliability between 4–6 weeks and 6-months postpartum (rs = .51). PDS showed high concurrent validity with other measures of postpartum psychopathology, rs(829) = .60 for depression and rs(829) = .61 for anxiety. Satisfactory diagnostic agreement was observed between diagnoses obtained by PDS and SCID, with good sensitivity (92%) and specificity (76%). Exploratory and confirmatory factor analyses revealed that the latent structure of birth-related PTSD was best identified by a three-factor model: re-experiencing and avoidance (RA), numbing and dysphoric-arousal (NDA) and dysphoric-arousal and anxious-arousal symptoms (DAA). Conclusions: The findings supported use of PDS as an effective screening measure for birth-related PTSD among postpartum women

Bimodal Phase Diagram of the Superfluid Density in LaAlO3/SrTiO3 Revealed by an Interfacial Waveguide Resonator

We explore the superconducting phase diagram of the two-dimensional electron system at the LaAlO3/SrTiO3 interface by monitoring the frequencies of the cavity modes of a coplanar waveguide resonator fabricated in the interface itself. We determine the phase diagram of the superconducting transition as a function of temperature and electrostatic gating, finding that both the superfluid density and the transition temperature follow a dome shape, but that the two are not monotonically related. The ground state of this 2DES is interpreted as a Josephson junction array, where a transition from long- to short-range order occurs as a function of the electronic doping. The synergy between correlated oxides and superconducting circuits is revealed to be a promising route to investigate these exotic compounds, complementary to standard magneto-transport measurements.Comment: 5 pages, 4 figures and 10 pages of supplementary materia

Water distribution in shocked regions of the NGC1333-IRAS4A protostellar outflow

We present the study of the H2O spatial distribution at two bright shocked regions along IRAS4A, one of the strongest H2O emitters among the Class 0 outflows. We obtained Herschel-PACS maps of the IRAS4A outflow and HIFI observations of two shocked positions. The largest HIFI beam of 38 arcsec at 557 GHz was mapped in several key water lines with different upper energy levels, to reveal possible spatial variations of the line profiles. We detect four H2O lines and CO (16-15) at the two selected positions. In addition, transitions from related outflow and envelope tracers are detected. Different gas components associated with the shock are identified in the H2O emission. In particular, at the head of the red lobe of the outflow, two distinct gas components with different excitation conditions are distinguished in the HIFI emission maps: a compact component, detected in the ground-state water lines, and a more extended one. Assuming that these two components correspond to two different temperature components observed in previous H2O and CO studies, the excitation analysis of the H2O emission suggests that the compact (about 3 arcsec) component is associated with a hot (T~1000 K) gas with densities ~(1-4)x10^5 cm^{-3}, whereas the extended one (10-17 arcsec) traces a warm (T~300-500 K) and dense gas (~(3-5)x10^7 cm^{-3}). Finally, using the CO (16-15) emission observed at R2, we estimate the H2O/H2 abundance of the warm and hot components to be (7-10)x10^{-7} and (3-7)x10^{-5}. Our data allowed us, for the first time, to resolve spatially the two temperature components previously observed with HIFI and PACS. We propose that the compact hot component may be associated with the jet that impacts the surrounding material, whereas the warm, dense, and extended component originates from the compression of the ambient gas by the propagating flow.Comment: 13 pages, 11 figures. Accepted for publication in Astronomy and Astrophysic

The Vibrio cholerae virulence regulatory cascade controls glucose uptake through activation of TarA, a small regulatory RNA

Vibrio cholerae causes the severe diarrhoeal disease cholera. A cascade of regulators controls expression of virulence determinants in V. cholerae at both transcriptional and post-transcriptional levels. ToxT is the direct transcription activator of the major virulence genes in V. cholerae . Here we describe TarA, a highly conserved, small regulatory RNA, whose transcription is activated by ToxT from toxboxes present upstream of the ToxT-activated gene tcpI . TarA regulates ptsG , encoding a major glucose transporter in V. cholerae . Cells overexpressing TarA exhibit decreased steady-state levels of ptsG mRNA and grow poorly in glucose-minimal media. A mutant lacking the ubiquitous regulatory protein Hfq expresses diminished TarA levels, indicating that TarA likely interacts with Hfq to regulate gene expression. RNAhybrid analysis of TarA and the putative ptsG mRNA leader suggests potential productive base-pairing between these two RNA molecules. A V. cholerae mutant lacking TarA is compromised for infant mouse colonization in competition with wild type, suggesting a role in the in vivo fitness of V. cholerae . Although somewhat functionally analogous to SgrS of Escherichia coli , TarA does not encode a regulatory peptide, and its expression is activated by the virulence gene pathway in V. cholerae and not by glycolytic intermediates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79165/1/j.1365-2958.2010.07397.x.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/79165/2/MMI_7397_sm_TableS1.pd

Thermal conductivity control by oxygen defect concentration modification in reducible oxides: The case of Pr0.1Ce0.9O2−δ thin films

We demonstrate the impact on thermal conductivity of varying the concentration of oxygen vacancies and reduced cations in Pr[subscript 0.1]Ce[subscript 0.9]O[subscript 2−δ] thin films prepared by pulsed laser deposition. The oxygen vacancy concentration is controlled by varying the oxygen partial pressure between 1 × 10[superscript −4] and 1 atm at 650  °C. Corresponding changes in the oxygen non-stoichiometry (δ) are monitored by detecting the lattice parameters of the films with high-resolution X-ray diffraction, while the thermal properties are characterized by time-domain thermoreflectance measurements. The films are shown to exhibit a variation in oxygen vacancy content, and in the Pr[superscript 3+]/Pr[superscript 4+] ratio, corresponding to changes in δ from 0.0027 to 0.0364, leading to a reduction in the thermal conductivity from k = 6.62 ± 0.61 to 3.82 ± 0.51 W/m-K, respectively. These values agree well with those predicted by the Callaway and von Baeyer model for thermal conductivity in the presence of point imperfections. These results demonstrate the capability of controlling thermal conductivity via control of anion and cation defect concentrations in a given reducible oxide.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (MRSEC Program, Award No. DMR-0819762

Tailoring non-stoichiometry and mixed ionic-electronic conductivity in nanostructured Pr-substituted ceria

High concentrations of mobile oxygen vacancies are crucial for devices such as SOFCs, SOECs, gas permeation membranes, and sensors, while for other applications such as ferroelectrics and piezoelectrics, oxygen vacancies are detrimental. Hence there is great interest in tailoring the oxygen vacancy concentration and mobility for given materials. Changes in oxygen non-stoichiometry also result in dilation of the crystal lattice, known as chemical expansion, and therefore there is a coupling between the electrical, chemical, and mechanical properties known as electro-chemo-mechanical coupling. Confined systems, such as thin films, are being investigated as a way to tailor the non-stoichiometry and transport properties of materials, shifting the paradigm away from searching for new materials or compositions. Please click Additional Files below to see the full abstract