Theory and design of Inx_{x}Ga1−x_{1-x}As1−y_{1-y}Biy_{y} mid-infrared semiconductor lasers: type-I quantum wells for emission beyond 3 μ\mum on InP substrates

We present a theoretical analysis and optimisation of the properties and performance of mid-infrared semiconductor lasers based on the dilute bismide alloy In$_{x}$Ga$_{1-x}$As$_{1-y}$Bi$_{y}$, grown on conventional (001) InP substrates. The ability to independently vary the epitaxial strain and emission wavelength in this quaternary alloy provides significant scope for band structure engineering. Our calculations demonstrate that structures based on compressively strained In$_{x}$Ga$_{1-x}$As$_{1-y}$Bi$_{y}$ quantum wells (QWs) can readily achieve emission wavelengths in the 3 -- 5 $\mu$m range, and that these QWs have large type-I band offsets. As such, these structures have the potential to overcome a number of limitations commonly associated with this application-rich but technologically challenging wavelength range. By considering structures having (i) fixed QW thickness and variable strain, and (ii) fixed strain and variable QW thickness, we quantify key trends in the properties and performance as functions of the alloy composition, structural properties, and emission wavelength, and on this basis identify routes towards the realisation of optimised devices for practical applications. Our analysis suggests that simple laser structures -- incorporating In$_{x}$Ga$_{1-x}$As$_{1-y}$Bi$_{y}$ QWs and unstrained ternary In$_{0.53}$Ga$_{0.47}$As barriers -- which are compatible with established epitaxial growth, provide a route to realising InP-based mid-infrared diode lasers.Comment: Submitted versio

Inside the Bondi radius of M87

Chandra X-ray observations of the nearby brightest cluster galaxy M87 resolve the hot gas structure across the Bondi accretion radius of the central supermassive black hole, a measurement possible in only a handful of systems but complicated by the bright nucleus and jet emission. By stacking only short frame-time observations to limit pileup, and after subtracting the nuclear PSF, we analysed the X-ray gas properties within the Bondi radius at 0.12-0.22 kpc (1.5-2.8 arcsec), depending on the black hole mass. Within 2 kpc radius, we detect two significant temperature components, which are consistent with constant values of 2 keV and 0.9 keV down to 0.15 kpc radius. No evidence was found for the expected temperature increase within ~0.25 kpc due to the influence of the SMBH. Within the Bondi radius, the density profile is consistent with $\rho\propto r^{-1}$. The lack of a temperature increase inside the Bondi radius suggests that the hot gas structure is not dictated by the SMBH's potential and, together with the shallow density profile, shows that the classical Bondi rate may not reflect the accretion rate onto the SMBH. If this density profile extends in towards the SMBH, the mass accretion rate onto the SMBH could be at least two orders of magnitude less than the Bondi rate, which agrees with Faraday rotation measurements for M87. We discuss the evidence for outflow from the hot gas and the cold gas disk and for cold feedback, where gas cooling rapidly from the hot atmosphere could feed the cirumnuclear disk and fuel the SMBH. At 0.2 kpc radius, the cooler X-ray temperature component represents ~20% of the total X-ray gas mass and, by losing angular momentum to the hot gas component, could provide a fuel source of cold clouds within the Bondi radius.Comment: 14 pages, 8 figures, accepted by MNRA

Solid state television camera system Patent

Solid state television camera system consisting of monolithic semiconductor mosaic sensor and molecular digital readout system

Natural history contributions of the University of Glasgow Exploration Society to Scotland and the World

Expeditions with a natural history focus have been organised by University of Glasgow staff and students since the 1930s. The educational benefits of such expeditions to students have been reported by Harper et al. ( Journal of Biological Education 51, 3- 16; 2017). Here, we present a short history of these expeditions, concentrating on their scientific achievements. In addition to expedition reports, a large number of PhD theses, masters and honours project reports and scientific papers have been based on expedition work. Many biological specimens have been deposited in museums, including some new species. We provide case histories of four expedition locations, to demonstrate the variety of work done, and the value of returning many times to the same place: Scotland, Trinidad and Tobago, North Cyprus and Ecuador. A major problem for expeditions is funding. For many years, the Carnegie Trust for the Universities of Scotland ran a funding stream that was crucial to the viability of Scottish university expeditions, but this has sadly now closed. For Glasgow University expeditions, the Blodwen Lloyd Binns Bequest has provided a reliable source since 1994, and we hope that it will continue to do so

Impact of alloy disorder on the band structure of compressively strained GaBiAs

The incorporation of bismuth (Bi) in GaAs results in a large reduction of the band gap energy (E$_g$) accompanied with a large increase in the spin-orbit splitting energy ($\bigtriangleup_{SO}$), leading to the condition that $\bigtriangleup_{SO} > E_g$ which is anticipated to reduce so-called CHSH Auger recombination losses whereby the energy and momentum of a recombining electron-hole pair is given to a second hole which is excited into the spin-orbit band. We theoretically investigate the electronic structure of experimentally grown GaBi$_x$As$_{1-x}$ samples on (100) GaAs substrates by directly comparing our data with room temperature photo-modulated reflectance (PR) measurements. Our atomistic theoretical calculations, in agreement with the PR measurements, confirm that E$_g$ is equal to $\bigtriangleup_{SO}$ for $\textit{x} \approx$ 9$$. We then theoretically probe the inhomogeneous broadening of the interband transition energies as a function of the alloy disorder. The broadening associated with spin-split-off transitions arises from conventional alloy effects, while the behaviour of the heavy-hole transitions can be well described using a valence band-anticrossing model. We show that for the samples containing 8.5% and 10.4% Bi the difficulty in identifying a clear light-hole-related transition energy from the measured PR data is due to the significant broadening of the host matrix light-hole states as a result of the presence of a large number of Bi resonant states in the same energy range and disorder in the alloy. We further provide quantitative estimates of the impact of supercell size and the assumed random distribution of Bi atoms on the interband transition energies in GaBi$_{x}$As$_{1-x}$. Our calculations support a type-I band alignment at the GaBi$_x$As$_{1-x}$/GaAs interface, consistent with recent experimental findings

Editorial: Community Series in Tools, Techniques, and Strategies for Teaching in a Real-world Context with Microbiology, Volume II

This Research Topic is the second volume in the Community Series Tools, Techniques, and Strategies for Teaching in a Real-World Context with Microbiology. Making microbiology relevant to our students increases student engagement with science, which could not be more important as we emerge from the COVID-19 pandemic. We have learned much during this period as we adapted and modified our learning environments and strategies, all while demonstrating the many ways microbes impact our world beyond disease. Placing microbes at center stage leads to engaging and exciting curricula and assignments. Microbes also are wonderful tools as they are easy to manipulate in the laboratory and serve as model organisms helping us to study biological phenomena and concepts. As faculty we can engage our students through guided inquiry, tactile hands-on tools, authentic research experiences, project-based learning, and case studies, with valuable, student-centered experiences occurring both inside and outside the classroom. We can also endeavor to abide by the principles of equity, diversity, and inclusion and those of universal design allowing all students to succeed in our courses

The Search for Signatures Of Transient Mass Loss in Active Stars

The habitability of an exoplanet depends on many factors. One such factor is the impact of stellar eruptive events on nearby exoplanets. Currently this is poorly constrained due to heavy reliance on solar scaling relationships and a lack of experimental evidence. Potential impacts of Coronal Mass Ejections (CMEs), which are a large eruption of magnetic field and plasma from a star, are space weather and atmospheric stripping. A method for observing CMEs as they travel though the stellar atmosphere is the type II radio burst, and the new LOw Frequency ARray (LOFAR) provides a means for detection. We report on 15 hours of observation of YZ Canis Minoris (YZ CMi), a nearby M dwarf flare star, taken in LOFAR's beam-formed observation mode for the purposes of measuring transient frequency-dependent low frequency radio emission. The observations utilized Low-Band Antenna (10-90 MHz) or High-Band Antenna (110-190 MHz) for five three-hour observation periods. In this data set, there were no confirmed type II events in this frequency range. We explore the range of parameter space for type II bursts constrained by our observations Assuming the rate of shocks is a lower limit to the rate at which CMEs occur, no detections in a total of 15 hours of observation places a limit of $\nu_{type II} < 0.0667$ shocks/hr $\leq \nu_{CME}$ for YZ CMi due to the stochastic nature of the events and limits of observational sensitivity. We propose a methodology to interpret jointly observed flares and CMEs which will provide greater constraints to CMEs and test the applicability of solar scaling relations

Interferometric Detection of Linear Polarization from Sagittarius A* at 230 GHz

We measured the linear polarization of Sagittarius A* to be 7.2 +/- 0.6 % at 230 GHzusing the BIMA array with a resolution of 3.6 x 0.9 arcsec. This confirms the previously reported detection with the JCMT 14-m antenna. Our high resolution observations demonstrate that the polarization does not arise from dust but from a synchrotron source associated with Sgr A*. We see no change in the polarization position angle and only a small change in the polarization fraction in four observations distributed over 60 days. We find a position angle 139 +/- 4 degrees that differs substantially from what was found in earlier JCMT observations at the same frequency. Polarized dust emission cannot account for this discrepancy leaving variability and observational error as the only explanations. The BIMA observations alone place an upper limit on the magnitude of the rotation measure of 2 x 10^6 rad m^-2. These new observations when combined with the JCMT observations at 150, 375 and 400 GHz suggest RM =-4.3 +/- 0.1 x 10^5 rad m^-2. This RM may be caused by an external Faraday screen. Barring a special geometry or a high number of field reversals, this RM rules out accretion rates greater than ~ 10^-7 M_sun y^-1. This measurement is inconsistent with high accretion rates necessary in standard advection dominated accretion flow and Bondi-Hoyle models for Sgr A*. It argues for low accretion rates as a major factor in the overall faintness of Sgr A*.Comment: accepted for publication in ApJ, 18 pages, 4 figure

The Equation of State of Neutron-Star Matter in Strong Magnetic Fields

We study the effects of very strong magnetic fields on the equation of state (EOS) in multicomponent, interacting matter by developing a covariant description for the inclusion of the anomalous magnetic moments of nucleons. For the description of neutron star matter, we employ a field-theoretical approach which permits the study of several models which differ in their behavior at high density. Effects of Landau quantization in ultra-strong magnetic fields ($B>10^{14}$ Gauss) lead to a reduction in the electron chemical potential and a substantial increase in the proton fraction. We find the generic result for $B>10^{18}$ Gauss that the softening of the EOS caused by Landau quantization is overwhelmed by stiffening due to the incorporation of the anomalous magnetic moments of the nucleons. In addition, the neutrons become completely spin polarized. The inclusion of ultra-strong magnetic fields leads to a dramatic increase in the proton fraction, with consequences for the direct Urca process and neutron star cooling. The magnetization of the matter never appears to become very large, as the value of $|H/B|$ never deviates from unity by more than a few percent. Our findings have implications for the structure of neutron stars in the presence of large frozen-in magnetic fields.Comment: 40 pages, 7 figures, accepted for publication in Ap

Effects of Feeding Legume Silage With Differing Tannin Levels on Lactating Dairy Cattle

Condensed tannins (CT) bind to plant proteins in the rumen, reducing protein degradation to ammonia and increasing milk production and milk protein (e.g. Waghorn, 1987). Previous research showed that the reduced soluble non-protein nitrogen (NPN) content of red clover (Trifolium pratense) silage (RCS) was related to its greater N efficiency relative to lucerne (Medicago sativa) silage (LS) (Broderick et al., 2001). Commercial cultivars of birdsfoot trefoil (Lotus corniculatus; BFT) contain modest levels of CT which reduce NPN formation in silage (Albrecht & Muck, 1991). The objective was to compare silages made from BFT with RCS and LS for milk production and N efficiency in lactating dairy cows