Formation of a high quality two-dimensional electron gas on cleaved GaAs

We have succeeded in fabricating a two-dimensional electron gas (2DEG) on the cleaved (110) edge of a GaAs wafer by molecular beam epitaxy (MBE). A (100) wafer previously prepared by MBE growth is reinstalled in the MBE chamber so that an in situ cleave exposes a fresh (110) GaAs edge for further MBE overgrowth. A sequence of Si-doped AlGaAs layers completes the modulation-doped structure at the cleaved edge. Mobilities as high as 6.1×10^5 cm^2/V s are measured in the 2DEG at the cleaved interface

Three-Body Kick to a Bright Quasar out of Its Galaxy During a Merger

The quasar HE0450-2958 was recently discovered to reside ~7kpc away from a galaxy that was likely disturbed by a recent merger. The lack of a massive spheroid of stars around the quasar raised the unlikely suggestion that it may have formed in a dark galaxy. Here we explain this discovery as a natural consequence of a dynamical kick imparted to the quasar as it interacted with a binary black hole system during a galaxy merger event. The typical stalling radius for a ~10^9 solar mass binary provides a kick of order the escape velocity of the stellar spheroid, bringing the quasar out to around the observed radius before it turns around. This is consistent with the observed low relative velocity between the quasar and the merger-remnant galaxy. The gas carried with the black hole throughout the three-body interaction fuels the quasar for the duration of its journey, ~2x10^7 years. Gravitational radiation recoil could not have produced the required kick.Comment: 5 pages, 2 figures, ApJ Letters, in pres

Dynamical dark energy from extra dimensions

We consider multidimensional cosmological model with a higher-dimensional product manifold M = R x R^{d_0} x H^{d_1}/\Gamma where R^{d_0} is d_0-dimensional Ricci-flat external (our) space and H^{d_1}/\Gamma is d_1-dimensional compact hyperbolic internal space. M2-brane solution for this model has the stage of accelerating expansion of the external space. We apply this model to explain the late time acceleration of our Universe. Recent observational data (the Hubble parameter at the present time and the redshift when the deceleration parameter changes its sign) fix fully all free parameters of the model. As a result, we find that considered model has too big size of the internal space at the present time and variation of the effective four-dimensional fine structure constant strongly exceeds the observational limits.Comment: 5 pages, 3 figures, LaTex, a few remarks and reference adde

A VLA Census of the Galactic H II Region Population

The Milky Way contains thousands of H II region candidates identified by their characteristic mid-infrared morphology, but lacking detections of ionized gas tracers such as radio continuum or radio recombination line emission. These targets thus remain unconfirmed as H II regions. With only $\sim$2500 confirmed H II regions in the Milky Way, Galactic surveys are deficient by several thousand nebulae when compared to external galaxies with similar star formation rates. Using sensitive 9 GHz radio continuum observations with the Karl G. Jansky Very Large Array (VLA), we explore a sample of H II region candidates in order to set observational limits on the actual total population of Galactic H II regions. We target all infrared-identified "radio quiet" sources from the WISE Catalog of Galactic H II regions between $245^{\circ}\geq\ell\geq90^{\circ}$ with infrared diameters less than 80$^{\prime\prime}$. We detect radio continuum emission from 50% of the targeted H II region candidates, providing strong evidence that most of the radio quiet candidates are bona fide HII regions. We measure the peak and integrated radio flux densities and compare the inferred Lyman continuum fluxes using models of OB-stars. We conclude that stars of approximately spectral type B2 and earlier are able to create H II regions with similar infrared and radio continuum morphologies as the more luminous H II regions created by O-stars. From our 50% detection rate of "radio quiet" sources, we set a lower limit of $\sim$7000 for the H II region population of the Galaxy. Thus the vast majority of the Milky Way's H II regions remain to be discovered.Comment: 11 pages of text, 146 infrared/radio images of faint HII region candidate

Photoreactive Stapled BH3 Peptides to Dissect the BCL-2 Family Interactome

SummaryDefining protein interactions forms the basis for discovery of biological pathways, disease mechanisms, and opportunities for therapeutic intervention. To harness the robust binding affinity and selectivity of structured peptides for interactome discovery, we engineered photoreactive stapled BH3 peptide helices that covalently capture their physiologic BCL-2 family targets. The crosslinking α helices covalently trap both static and dynamic protein interactors, and enable rapid identification of interaction sites, providing a critical link between interactome discovery and targeted drug design

Compensatory changes in female running mechanics during a simulated 10 km race

During a 10 km run at race pace, changes in lower extremity mechanics have been reported in male runners however mechanical changes over 10 km in female runners is unknown. Thus we aimed to examine running mechanics in females during a simulated 10 km race on a treadmill. Nine female distance runners (age: 32.1±4.2 yrs; ht: 166.7 ± 7.4 cm; wt: 57.8 ± 7.0 kg; VO2max = 3.24 ± 0.50 L/min) completed graded exercise testing (Day 1); 10km time trial (Day 2); and simulated 10km treadmill run (DAY 3; 95 % of running velocity from Day 2 time-trial). Mechanical data sampled at 120Hz using a 6-camera optoelectronic motion capture system and effort (Rating of Perceived Exertion - RPE) were measured at 50, 1450, 2950, 4450, 5950, 7450, 8950 and 9950 metres. Maximum voluntary contraction of knee extensors was measured pre-post. Seven participants decreased MVC (1-21% decrease) and RPE increased from 12 (50m) to 19 (9950m). Step frequency decreased 3 steps/min (p<0.05) and step length increased 3cm. Max knee extension and max knee flexion increased from 50m to 9950m and hip height was lowered over the 10km time-trial. These results indicate that whole body fatigue influences RPE and is associated with mechanical changes to maintain pace in female runners. Specifically, the combination of knee extension and knee flexion increases likely reduces limb inertia as the runner fatigues minimizing decreases in step frequency and improving step length. These results are the first to illuminate the fatigue related intrinsic coping mechanisms of female runners at race pace

The impact of direct-to-home telemedicine visits on parent, physician, and therapist experience for children with special healthcare needs

To examine the experience of parents, therapists, and physiatrists on direct-to-home tele-physiatry visits with the goal of informing future use of telemedicine for children with special healthcare needs

A SCUBA survey of the NGC 2068/2071 protoclusters

We report the results of a submillimeter dust continuum survey of the protoclusters NGC 2068 and NGC 2071 in Orion B carried out at 850 microns and 450 microns with SCUBA on JCMT. The mapped region is ~ 32' x 18' in size (~ 4 pc x 2 pc) and consists of filamentary dense cores which break up into small-scale (~ 5000 AU) fragments, including 70 starless condensations and 5 circumstellar envelopes/disks. The starless condensations, seen on the same spatial scales as protostellar envelopes, are likely to be gravitationally bound and pre-stellar in nature. Their mass spectrum, ranging from ~ 0.3 Msun to ~ 5 Msun, is reminiscent of the stellar initial mass function (IMF). Their mass-size relation suggests that they originate from gravitationally-driven fragmentation. We thus argue that pre-collapse cloud fragmentation plays a major role in shaping the IMF.Comment: 6 pages, 4 figures, 1 table. Letter accepted by Astronomy & Astrophysic