Physics

The unfolding of a protein by the application of an external force pulling two atoms of the protein can be detected by atomic force and optical tweezers technologies as have been broadly demonstrated in the past decade. Variation of the applied force results in a modulation of the free-energy barrier to unfolding and thus, the rate of the process, which is often assumed to have single exponential kinetics. It has been recently shown that it is experimentally feasible, through the use of force clamps, to estimate the distribution of unfolding times for a population of proteins initially in the native state. In this Letter we show how the analysis of such distributions under a range of forces can provide unique information about the underlying free-energy surface such as the height of the free-energy barrier, the preexponential factor and the force dependence of the unfolding kinetics without resorting to ad hoc kinetic models.

Using SANS to map the deformation of individual polymer chains in the vicinity of re-entrant corners in a contraction-expansion flow, we show that stress singularities at such corners, predicted by formulations of fluid dynamics that lack a molecular basis, do not cause extreme deformation of the chains. Multiscale modeling based on a nonlinear tube theory incorporating appropriate relaxation processes quantitatively reproduces the observed scattering, thus providing further evidence for the universality of the tube model for polymer flow.

We first show that the new Wilkinson Microwave Anisotropy Probe (WMAP) 3-yr data confirm the detection by Myers et al. of an extended SZ signal centred on 606 Abell (ACO) clusters with richness class, R >= 2. Our results also show SZ decrements around APM and 2MASS groups at increased significance than previously detected. We then follow the approach of Lieu, Mittaz & Zhang and compare the stacked WMAP results for the decrement in 31 clusters with ROSAT X-ray profiles where Lieu et al. found on average less SZ decrement in the WMAP 1-yr data than predicted. We confirm that in the 3-yr data these same clusters again show less SZ decrement than the X-ray data predict. We then analysed the WMAP results for the 38 X-ray clusters with OVRO/BIMA measured SZ decrements as presented by Bonamente et al.. We again find that the average decrement is measured to be significantly less (5.5σ) than predicted by the Chandra X-ray data. Thus while we confirm the original detection of an extended SZ effect by Myers et al., these X-ray comparisons may now suggest that the central SZ amplitudes detected by WMAP may actually be lower than expected. One possible explanation is that there is contamination of the WMAP SZ signal by radio sources in the clusters but we argue that this appears implausible. We then consider the possibility that the SZ decrement has been lensed away by foreground galaxy groups. Such a model predicts that the SZ decrement should depend on cluster redshift. A reduction in the SZ decrement with redshift is suggested from the ACO cluster sample and also from comparing the samples of Lieu et al. and Bonamente et al.. However, the mass power spectrum would require a far higher amplitude than currently expected if lensing was to explain the SZ deficit in high-redshift clusters.

Given the present, relatively limited deployment of low cost and mass space missions, there are clear opportunities for the application of small-scale propulsion systems in further enabling these small satellite missions. With this situation in mind, a team comprising ASTC, SSTL, TNO and QinetiQ – under funding from the European Space Agency – has undertaken the development of a MEMS-based micro-rocket engine concept with the intended capability of providing a specific impulse of greater than 100s. Both turbo-pump fed bi-propellant as well as mono propellant concepts were investigated. For demonstration a mono-propellant design was selected of which an initial design concept was developed, based on hydrogen peroxide decomposition. Identified as the critical component in the mono-propellant system, several batches of the honeycomb wafers – upon which the decomposition occurs – have been manufactured. As a proof of concept, the wafers have been subjected to a set of structural and functionality tests. Given the results of the latest testing initiative, it is envisaged that, with adequate refinement and development of the current design, a reliable and deployable mono-propellant micro-rocket engine solution may be realised.

We investigate the use of simple colour cuts applied to the Sloan Digital Sky Survey (SDSS) optical imaging to perform photometric selections of emission line galaxies out to z < 1. Our selection is aimed at discerning three separate redshift ranges: 0.2<z<0.4, 0.4<z<0.6 and 0.6<z<1.0. We calibrate the selections using data taken by the COMBO-17 survey in a single field (S11), which is covered by the SDSS imaging. We thus perform colour-cuts using the SDSS g, r and i bands and obtain mean photometric redshifts of zlow = 0.32 ± 0.08, zmid = 0.44 ± 0.12 and zhi = 0.65 ± 0.21. We further calibrate our high redshift selection using spectroscopic observations with the AAOmega spectrograph on the 4m Anglo-Australian Telescope (AAT), observing ≈ 50 − 200 galaxy candidates in 4 separate fields. With just 1-hour of integration time and with seeing of ≈ 1.6′′, we successfully determined redshifts for ≈ 65% of the targeted candidates. We compare our spectroscopic redshifts to the photometric redshifts from the COMBO-17 survey and find reasonable agreement between the two. We calculate the angular correlation functions of these samples and find correlation lengths of r0 = 2.64±0.08 Mpc/h, r0 = 3.62±0.06 Mpc/h and r0 = 5.88±0.12 Mpc/h for the low, mid and high redshift samples respectively. Comparing these results with predicted dark matter clustering, we estimate the bias parameter for each sample to be b = 0.70, b = 0.92 and b = 1.46. We calculate the 2-point redshift-space correlation function at z ≈ 0.6 and find a clustering amplitude of so = 6.4±0.8 Mpc/h. Finally, we use our photometric sample to search for the Integrated Sachs-Wolfe signal in the WMAP 5yr data. We cross-correlate our three redshift samples with the WMAP W, V, Q and K bands and find an overall trend for a positive signal similar to that expected from models. However, the signal in each is relatively weak with the results in the WMAP W-band of wTg(< 100′) = 0.25±0.27 µK, 0.17±0.20 µK and 0.17±0.16 µK for the low, mid and high redshift samples respectively. Combining all three galaxy samples we find a signal of wTg(<100′) = 0.20±0.12 µK in the WMAP W-band, a significance of 1.7σ. However, in testing for systematics where the WMAP data is rotated with respect to the ELG sample, we found similar results at several different rotation angles, implying the apparent signal may be produced by systematic effects.

Experimental ground testing has been carried out to determine whether digital latches can spontaneously change state in severe (space weather induced) outer-belt environments via the mechanism of internal spacecraft charging/discharging. A new facility is employed which improves simulations of the charging environment experienced by satellite equipment and materials. Results are presented which demonstrate the complete chain of events from environment to circuit anomaly. The anomaly rate shows dependence on both charging flux and circuit board temperature.

Aims. We use a combination of CFHTLS deep optical data, WIRCam Deep Survey (WIRDS) near-infrared data and XMM-Newton survey data to identify z > 1.1 clusters in the CFHTLS D1 and D4 fields. Counterparts to such clusters can not be identified without deep near-infrared data and as such the total of ≈ 1deg2 of J , H and Ks band imaging provided by WIRDS is an indispensable tool in such work.

Methods. Using public XMM X-ray data, we identify extended X-ray sources in the two fields. The resulting catalogue of extended X-ray sources was then analyzed for optical/near-infrared counterparts, using a red-sequence algorithm applied to the deep optical and near-infrared data. Redshifts of candidate groups and clusters were estimated using the median photometric redshifts of detected counterparts and where available these were combined with spectroscopic data (from VVDS Deep and Ultra-Deep and using AAT AAOmega data). Additionally, we surveyed X-ray point sources for potential group systems at the limit of our detection range in the X-ray data. A catalogue of z > 1.1 cluster candidates in the two fields has been compiled and cluster masses, radii and temperatures have been estimated using the scaling relations.

Results. The catalogue of group and cluster candidates consists of 15 z > 1.1 objects. We find several massive clusters ( M > 10^14 M⊙ ) and a number of lower mass clusters/groups. Three of the detections are previously published extended X-ray sources. Of note is JKSC 041 (previously detected via Chandra X-ray data and reported as a z = 1.9 cluster based on UKIDSS infrared imaging) for which we identify a number of structures at redshifts of z = 0.8, z = 0.96, z = 1.13 and z = 1.49 (but see no evidence of a structure at z = 1.9). We also make an independent detection of the massive cluster, XMMXCS J2215.9-1738, for which we estimate a redshift of z = 1.37 (compared to the spectroscopically confirmed redshift of z = 1.45). We use the z > 1.1 catalogue to compare the cluster number counts in these fields with models based on WMAP 7-year cosmology and find that the models slightly over-predict the observations, whilst at z > 1.5 we do not detect any clusters. We note that cluster number counts at z > 1.1 are highly sensitive to the cosmological model, however a significant reduction in present statistical (due to available survey area) and systematic (due to cluster scaling relations) uncertainties is required in order to confidently constrain cosmological parameters using cluster number counts at high redshift.

We present the initial imaging and spectroscopic data acquired as part of the VLT VIMOS Lyman-break galaxy Survey. U BR (or U BV I ) imaging covers five ≈ 36′ × 36′ fields centred on bright z > 3 QSOs, allowing ≈ 21, 000 2 < z < 3.5 galaxy candidates to be selected using the Lyman-break technique. We performed spectroscopic follow-up using VLT VIMOS, measuring redshifts for 1020 z > 2 Lyman-break galaxies and 10 z > 2 QSOs from a total of 19 VIMOS pointings. From the galaxy spectra, we observe a 625±510 km/s velocity offset between the interstellar absorption and Lyα emission line redshifts, consistent with previous results. Using the photometric and spectroscopic catalogues, we have analysed the galaxy clustering at z ≈ 3. The angular correlation function, w(θ), is well fit by a double power-law with clustering scale-length, r0 = 3.19 (+0.32−0.54) Mpc/h and slope γ = 2.45 for r < 1 Mpc/h and r0 = 4.37 (+0.43−0.55) Mpc/h with γ = 1.61 ± 0.15 at larger scales. Using the redshift sample we estimate the semi-projected correlation function, wp(σ) and, for a γ = 1.8 power-law, find r0 = 3.67 (+0.23−0.24) Mpc/h for the VLT sample and r0 = 3.98 (+0.14−0.15) Mpc/h for a combined VLT+Keck sample. From ξ (s) and ξ (σ, π), and assuming the above ξ(r) models, we find that the combined VLT and Keck surveys require a galaxy pairwise velocity dispersion of ≈ 700 km/s, higher than the ≈ 400 km/s assumed by previous authors. We also measure a value for the gravitational growth rate parameter of β(z = 3) = 0.48 ± 0.17, again higher than previously found and implying a low value for the bias of b = 2.06(+1.1−0.5). This value is consistent with the galaxy clustering amplitude which gives b = 2.22 ± 0.16, assuming the standard cosmology, implying that the evolution of the gravitational growth rate is also consistent with Einstein gravity. Finally, we have compared our Lyman-break galaxy clustering amplitudes with lower redshift measurements and find that the clustering strength is not inconsistent with that of low-redshift L ∗ spirals for simple ‘long-lived’ galaxy models.

We investigate the use of simple colour cuts applied to the Sloan Digital Sky Survey (SDSS) optical imaging to perform photometric selections of emission line galaxies out to z < 1. Our selection is aimed at discerning three separate redshift ranges: 0.2 z 0.4, 0.4 z 0.6 and 0.6 z 1.0. We calibrate the selections using data taken by the COMBO-17 survey in a single field (S11), which is covered by the SDSS imaging. We thus perform colour-cuts using the SDSS g, r and i bands and obtain mean photometric redshifts of z low = 0.32 ± 0.08, z mid = 0.44±0.12 and z hi = 0.65±0.21. We further calibrate our high redshift selection using spectroscopic observations with the AAOmega spectrograph on the 4m Anglo-Australian Telescope (AAT), observing ≈ 50 − 200 galaxy candidates in 4 separate fields. With just 1hour of integration time and with seeing of ≈ 1.6 ′′ , we successfully determined redshifts for ≈ 65% of the targeted candidates. We compare our spectroscopic redshifts to the photometric redshifts from the COMBO-17 survey and find reasonable agreement between the two. We calculate the angular correlation functions of these samples and find correlation lengths of r 0 = 2.64 +0.05 −0.08 h −1 M pc, r 0 = 3.62 ± 0.06h −1 M pc and r 0 = 5.88 ± 0.12h −1 M pc for the low, mid and high redshift samples respectively. Comparing these results with predicted dark matter clustering, we estimate the bias parameter for each sample to be b = 0.70, b = 0.92 and b = 1.46. We calculate the 2-point redshift-space correlation function at z ≈ 0.6 and find a clustering amplitude of s o = 6.4 ± 0.8h −1 M pc. Finally, we use our photometric sample to search for the Integrated Sachs-Wolfe signal in the WMAP 5yr data. We cross-correlate our three redshift samples with the WMAP W, V, Q and K bands and find an overall trend for a positive signal similar to that expected from models. However, the signal in each is relatively weak with the results in the WMAP W-band of w T g (< 100 ′ ) = 0.25 ± 0.27µK, 0.17 ± 0.20µK and 0.17 ± 0.16µK for the low, mid and high redshift samples respectively. Combining all three galaxy samples we find a signal of w T g (< 100 ′ ) = 0.20 ± 0.12µK in the WMAP W-band, a significance of 1.7σ. However, in testing for systematics where the WMAP data is rotated with respect to the ELG sample, we found similar results at several different rotation angles, implying the apparent signal may be produced by systematic effects.

Astronomical Science flowing gas powered by the star formation in the central region. In this way the Lyα emission is scattered and ab sorbed by outflowing material, leading to the asymmetry and the velocity offsets between emission and absorption lines.

Results. The VVDS-LAE sample reaches faint line fluxes F(Lya) = 1.5x1^18 erg/s/cm^2 (corresponding to L(Lya)=10^41 erg/s at z~3) enabling the faint end slope of the luminosity function to be constrained to a=-1.6+-0.12 at redshift z~2.5 and to a=-1.78+0.1-0.12 at z=4, placing on firm statistical grounds trends found in previous LAE studies, and indicating that sub-L* LAE contribute significantly to the SFRD. The projected number density and volume density of faint LAE in 2<z<6.6 with F>1.5x10^18 erg/s/cm^2 are 33 galaxies/arcmin^2 and 4x10^-2 Mpc^-3, respectively. We find that the the observed luminosity function of LAE does not evolve from z=2 to z=6. This implies that, after correction for the redshift-dependent IGM absorption, the intrinsic LF must have evolved significantly over 3 Gyr. The SFRD from LAE contributes to about 20% of the SFRD at z =2-3, while the LAE appear to be the dominant source of star formation producing ionizing photons in the early universe z>5-6, becoming equivalent to that of Lyman Break galaxies.

We present the results of a narrow-band (H2S1, λc= 2.121 μm, δλ= 0.021 μm) imaging search with Wide Field Camera/United Kingdom Infrared Telescope for Hα emitters (HAEs) around several potential signposts of rare (˜10-7-10-8 comoving Mpc-3) overdense regions at z = 2.23: an overdensity of quasi-stellar objects [QSOs; 2dF QSO Redshift Survey (2QZ) cluster], a powerful, high-redshift radio galaxy (HzRG) and a concentration of submillimetre galaxies (SMGs) and optically faint radio galaxies (OFRGs). In total, we detect 137 narrow-band emitter candidates down to emission-line fluxes of 0.5-1 × 10-16 erg s-1 cm-2, across a total area of 0.56 deg2 (2.1 × 105 comoving Mpc3 at z = 2.23) in these fields. The BzK colours of the emitters suggest that at least 80 per cent of our sample are likely to be HAEs at z = 2.23. This is one of the largest HAE samples known at z ≳ 2. Although there is no evidence for large-scale (20 comoving Mpc) overdensities of the emitters around the targets, we find modest (˜3σ) local overdensities associated with all three targets on smaller scales (5-10 comoving Mpc). In the 2QZ cluster field, the structure appears to be connecting the QSOs, while in the HzRG and SMG/OFRG fields, the structures are seen only in the vicinities of the targets. Our results suggest that these rare targets are located in local overdensities of galaxies, rather than average density regions, although it is not clear whether these structures are likely to evolve into rare, rich clusters. The K-band magnitudes and the Hα equivalent widths of the emitters are weakly correlated with the overdensities of the emitters: emitters in overdense regions are more evolved systems compared to those in underdense regions at z = 2.23. We find several examples of extended HAEs near to the targets, including a striking example with a spatial extent of 7.5 arcsec (60 kpc at z = 2.23) in the 2QZ cluster field, suggesting that these are relatively common in overdense regions. We conclude that narrow-band Hα surveys are efficient routes to map overdense regions at high redshifts and thus to understand the relation between the growth of galaxies and their surrounding large-scale structures. Based on observations obtained with the Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope (UKIRT), and in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and collected at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration.