Partial local density of states from scanning gate microscopy

Scanning gate microscopy images from measurements made in the vicinity of quantum point contacts were originally interpreted in terms of current flow. Some recent work has analytically connected the local density of states to conductance changes in cases of perfect transmission, and at least qualitatively for a broader range of circumstances. In the present paper, we show analytically that in any time-reversal invariant system there are important deviations that are highly sensitive to imperfect transmission. Nevertheless, the unperturbed partial local density of states can be extracted from a weakly invasive scanning gate microscopy experiment, provided the quantum point contact is tuned anywhere on a conductance plateau. A perturbative treatment in the reflection coefficient shows just how sensitive this correspondence is to the departure from the quantized conductance value and reveals the necessity of local averaging over the tip position. It is also shown that the quality of the extracted partial local density of states decreases with increasing tip radius.Comment: 16 pages, 9 figure

The Metal Abundances across Cosmic Time (MACT\mathcal{MACT}) Survey. II. Evolution of the Mass-Metallicity Relation over 8 Billion Years, using [OIII]λ\lambda4363\AA-based Metallicities

We present the first results from MMT and Keck spectroscopy for a large sample of $0.1\leq z\leq1$ emission-line galaxies selected from our narrow-band imaging in the Subaru Deep Field. We measured the weak [OIII]$\lambda$4363 emission line for 164 galaxies (66 with at least 3$\sigma$ detections, and 98 with significant upper limits). The strength of this line is set by the electron temperature for the ionized gas. Because the gas temperature is regulated by the metal content, the gas-phase oxygen abundance is inversely correlated with [OIII]$\lambda$4363 line strength. Our temperature-based metallicity study is the first to span $\approx$8 Gyr of cosmic time and $\approx$3 dex in stellar mass for low-mass galaxies, $\log{\left(M_{\rm star}/M_{\rm sun}\right)}\approx6.0-9.0$. Using extensive multi-wavelength photometry, we measure the evolution of the stellar mass--gas metallicity relation and its dependence on dust-corrected star formation rate (SFR). The latter is obtained from high signal-to-noise Balmer emission-line measurements. Our mass-metallicity relation is consistent with Andrews & Martini at $z\leq0.3$, and evolves toward lower abundances at a given stellar mass, $\log{({\rm O/H})}\propto(1+z)^{-2.32^{+0.52}_{-0.26}}$. We find that galaxies with lower metallicities have higher SFRs at a given stellar mass and redshift, although the scatter is large ($\approx$0.3 dex), and the trend is weaker than seen in local studies. We also compare our mass--metallicity relation against predictions from high-resolution galaxy formation simulations, and find good agreement with models that adopt energy- and momentum-driven stellar feedback. We have identified 16 extremely metal-poor galaxies with abundances less than a tenth of solar; our most metal-poor galaxy at $z\approx0.84$ is similar to I Zw 18.Comment: 18 pages, 11 figures, 2 tables. Updated to match published version in the Astrophysical Journa

Pinch Keyboard: Natural Text Input for Immersive Virtual Environments

Text entry may be needed for system control tasks in immersive virtual environments, but no efficient and usable techniques exist. We present the pinch keyboard interaction technique, which simulates a standard QWERTY keyboard using Pinch Gloves™ and 6 DOF trackers. The system includes visual and auditory feedback and a simple method of calibration

Cell Cycle Entry Control in Naïve and Memory CD8⁺ T Cells

CD8+ T cells play important roles in immunity and immuno-oncology. Upon antigen recognition and co-stimulation, naïve CD8+ T cells escape from dormancy to engage in a complex programme of cellular growth, cell cycle entry and differentiation, resulting in rapid proliferation cycles that has the net effect of producing clonally expanded, antigen-specific cytotoxic T lymphocytes (CTLs). A fraction of activated T cells will re-enter dormancy by differentiating into memory T cells, which have essential roles in adaptive immunity. In this review, we discuss the current understanding of cell cycle entry control in CD8+ T cells and crosstalk between these mechanisms and pathways regulating immunological phenotypes

Draft Genome Sequence of an Enterococcus faecalis ATCC 19433 Siphovirus Isolated from Raw Domestic Sewage.

We previously isolated and characterized an Enterococcus faecalis ATCC 19433 siphovirus from raw domestic sewage as a viral indicator of human fecal pollution. Here, we report the draft genome sequence of this bacteriophage

"Direct" Gas-phase Metallicities, Stellar Properties, and Local Environments of Emission-line Galaxies at Redshift below 0.90

Using deep narrow-band (NB) imaging and optical spectroscopy from the Keck telescope and MMT, we identify a sample of 20 emission-line galaxies (ELGs) at z=0.065-0.90 where the weak auroral emission line, [OIII]4363, is detected at >3\sigma. These detections allow us to determine the gas-phase metallicity using the "direct'' method. With electron temperature measurements and dust attenuation corrections from Balmer decrements, we find that 4 of these low-mass galaxies are extremely metal-poor with 12+log(O/H) <= 7.65 or one-tenth solar. Our most metal-deficient galaxy has 12+log(O/H) = 7.24^{+0.45}_{-0.30} (95% confidence), similar to some of the lowest metallicity galaxies identified in the local universe. We find that our galaxies are all undergoing significant star formation with average specific star formation rate (SFR) of (100 Myr)^{-1}, and that they have high central SFR surface densities (average of 0.5 Msun/yr/kpc^2. In addition, more than two-thirds of our galaxies have between one and four nearby companions within a projected radius of 100 kpc, which we find is an excess among star-forming galaxies at z=0.4-0.85. We also find that the gas-phase metallicities for a given stellar mass and SFR lie systematically below the local M-Z-(SFR) relation by \approx0.2 dex (2\sigma\ significance). These results are partly due to selection effects, since galaxies with strong star formation and low metallicity are more likely to yield [OIII]4363 detections. Finally, the observed higher ionization parameter and electron density suggest that they are lower redshift analogs to typical z>1 galaxies.Comment: Accepted for publication in the Astrophysical Journal (15 November 2013). 31 pages in emulateapj format with 16 figures and 7 tables. Revised to address referee's comments, which include discussion on selection effects, similarities to green pea galaxies, and nebular continuum contribution. Modifications were made for some electron temperature and metallicity measurement

An Attempt to Probe the Radio Jet Collimation Regions in NGC 4278, NGC 4374 (M84), and NGC 6166

NRAO Very Long Baseline Array (VLBA) observations of NGC 4278, NGC 4374 (M84), NGC 6166, and M87 (NGC 4486) have been made at 43 GHz in an effort to image the jet collimation region. This is the first attempt to image the first three sources at 43 GHz using Very Long Baseline Interferometry (VLBI) techniques. These three sources were chosen because their estimated black hole mass and distance implied a Schwarzschild radius with large angular size, giving hope that the jet collimation regions could be studied. Phase referencing was utilize for the three sources because of their expected low flux densities. M87 was chosen as the calibrator for NGC 4374 because it satisfied the phase referencing requirements: nearby to the source and sufficiently strong. Having observed M87 for a long integration time, we have detected its sub-parsec jet, allowing us to confirm previous high resolution observations made by Junor, Biretta & Livio, who have indicated that a wide opening angle was seen near the base of the jet. Phase referencing successfully improved our image sensitivity, yielding detections and providing accurate positions for NGC 4278, NGC 4374 and NGC 6166. These sources are point dominated, but show suggestions of extended structure in the direction of the large-scale jets. However, higher sensitivity will be required to study their sub-parsec jet structure

Spin-orbit coupling induced ultra-high harmonic generation from magnetic dynamics

The recent boost in data transfer rates puts a daring strain on information technology. Sustaining such a growth rate requires the development of sources, detectors and systems working in the so-called TeraHertz (THz) gap covering the frequency window from 0.1 to 10 THz (1 THz = 10$^{12}$~Hz). This gap represents a challenge for conventional electronic devices due to carrier transit delays ($\sim$1-10ps), as well as for photonic devices due to thermal fluctuations (300K$\sim$6THz). Nonetheless, designing efficient, room-temperature THz sources would constitute a key enabler to applications spanning from high-resolution imaging to extreme wide band wireless communication. Whereas high-harmonic generation in solid is usually limited to less than ten harmonics, broadband THz emission has been demonstrated using laser-induced superdiffusive spin currents in magnetic bilayers composed of a ferromagnet deposited on top of a noble metal. While promising, this technique presents the major disadvantage of necessitating optical pumping and hence lacks scalability. Here, we demonstrate that extremely high harmonic emission can be achieved by exploiting conventional spin pumping, without the need of optical excitation. We show that when the spin-orbit coupling strength is close to the s-d exchange energy, a strongly non linear regime resulting from resonant spin flip scattering occurs leading to the generation of a thousand of harmonics at realistic antiferromagnetic precession frequencies, thereby enhancing both spin and charge dynamics by two orders of magnitude, and allowing for an emission at frequencies above 300 THz.Comment: 7 pages, 6 figure