Strong electrically tunable exciton g-factors in an individual quantum dots due to hole orbital angular momentum quenching

Strong electrically tunable exciton g-factors are observed in individual (Ga)InAs self-assembled quantum dots and the microscopic origin of the effect is explained. Realistic eight band k.p simulations quantitatively account for our observations, simultaneously reproducing the exciton transition energy, DC Stark shift, diamagnetic shift and g-factor tunability for model dots with the measured size and a comparatively low In-composition of x(In)~35% near the dot apex. We show that the observed g-factor tunability is dominated by the hole, the electron contributing only weakly. The electric field induced perturbation of the hole wavefunction is shown to impact upon the g-factor via orbital angular momentum quenching, the change of the In:Ga composition inside the envelope function playing only a minor role. Our results provide design rules for growing self-assembled quantum dots for electrical spin manipulation via electrical g-factor modulation

Sorghum for Grain: Production Strategies in the Rolling Plains.

16 p

Subglacial bedform and moat initiation beneath Rutford Ice Stream, West Antarctica

The accuracy of sea-level rise predictions is highly dependent on reliably understanding the subglacial environment beneath ice streams. Bedforms result from the interaction between ice and its substrate, and therefore have the potential to shed light on poorly understood basal conditions influencing ice dynamics. However, theoretical models of bedform formation are often based on observations from deglaciated areas or from sparsely-sampled geophysical surveys over glaciated regions. Here, we use high-resolution three- and two-dimensional radar and seismic data to reveal details of the initiation and evolution of a subglacial bedform beneath Rutford Ice Stream, West Antarctica. Radar surveys at 20 m and 50 m line spacing allow detailed imaging of bed topography, including a moat up to 55 m deep, surrounding the upstream end of a 50-m high and >18-km long bedform. Many models rely on either a topographical or a locally resistant seed point to initiate bedform formation. The bedform described here is mostly composed of soft sediment (porosity >0.3) and lacks a boulder or outcrop, suggesting the bedform initiated without a topographic seed point. Sediment at the upstream end of bedforms appears stiffer over a distance of 2.3 km. We suggest sediment inhomogeneities in the initially flat bed cause the deposition of sediment, which, assuming resistant enough, acts as a seed point for bedform extension and moat erosion. The moat's geometry and its truncation of other bedforms suggest that it was eroded after the deposition of surrounding bedforms. These observations from a modern ice stream deliver information of subglacial processes involved in the initiation as well as in situ high-resolution topography and properties of bedforms and moats. Using these observations numerical models can be tested and developed accordingly

Observation of Parity Violation in the Omega-minus -> Lambda + K-minus Decay

The alpha decay parameter in the process Omega-minus -> Lambda + K-minus has been measured from a sample of 4.50 million unpolarized Omega-minus decays recorded by the HyperCP (E871) experiment at Fermilab and found to be [1.78 +/- 0.19(stat) +/- 0.16(syst)]{\times}10^{-2}. This is the first unambiguous evidence for a nonzero alpha decay parameter, and hence parity violation, in the Omega-minus -> Lambda + K-minus decay.Comment: 10 pages, 7 figure

Possible futures for groundwater in Burkina Faso under a changing climate

This narrative describes three possible future scenarios for water resources in Burkina Faso and the human and socio-economic impacts that might be experienced by people living in rural areas. The narratives aim to stimulate discussion towards realistic policy responses and the decision support tools needed to assist future planning needs. It is important to recognise that the scenarios do not represent every possible outcome projected by hydroclimate models, and resulting impacts will be contextualised by local circumstances. See here for information about BRAVE (www.walker.ac.uk) and the UPGro programme: upgro.org/consortium/brave2/

A glassy contribution to the heat capacity of hcp 4^4He solids

We model the low-temperature specific heat of solid $^4$He in the hexagonal closed packed structure by invoking two-level tunneling states in addition to the usual phonon contribution of a Debye crystal for temperatures far below the Debye temperature, $T < \Theta_D/50$. By introducing a cutoff energy in the two-level tunneling density of states, we can describe the excess specific heat observed in solid hcp $^4$He, as well as the low-temperature linear term in the specific heat. Agreement is found with recent measurements of the temperature behavior of both specific heat and pressure. These results suggest the presence of a very small fraction, at the parts-per-million (ppm) level, of two-level tunneling systems in solid $^4$He, irrespective of the existence of supersolidity.Comment: 11 pages, 4 figure

Hydroclimate footprint of pan-Asian monsoon water isotope during the last deglaciation

Oxygen isotope speleothem records exhibit coherent variability over the pan-Asian summer monsoon (AM) region. The hydroclimatic representation of these oxygen isotope records for the AM, however, has remained poorly understood. Here, combining an isotope-enabled Earth system model in transient experiments with proxy records, we show that the widespread AM delta O-18(c) signal during the last deglaciation (20 to 11 thousand years ago) is accompanied by a continental-scale, coherent hydroclimate footprint, with spatially opposite signs in rainfall. This footprint is generated as a dynamically coherent response of the AM system primarily to meltwater forcing and secondarily to insolation forcing and is further reinforced by atmospheric teleconnection. Hence, widespread delta O-18(p) depletion in the AM region is accompanied by a northward migration of the westerly jet and enhanced southwesterly monsoon wind, as well as increased rainfall from South Asia (India) to northern China but decreased rainfall in southeast China

HyperCP: A high-rate spectrometer for the study of charged hyperon and kaon decays

The HyperCP experiment (Fermilab E871) was designed to search for rare phenomena in the decays of charged strange particles, in particular CP violation in $\Xi$ and $\Lambda$ hyperon decays with a sensitivity of $10^{-4}$. Intense charged secondary beams were produced by 800 GeV/c protons and momentum-selected by a magnetic channel. Decay products were detected in a large-acceptance, high-rate magnetic spectrometer using multiwire proportional chambers, trigger hodoscopes, a hadronic calorimeter, and a muon-detection system. Nearly identical acceptances and efficiencies for hyperons and antihyperons decaying within an evacuated volume were achieved by reversing the polarities of the channel and spectrometer magnets. A high-rate data-acquisition system enabled 231 billion events to be recorded in twelve months of data-taking.Comment: 107 pages, 45 Postscript figures, 14 tables, Elsevier LaTeX, submitted to Nucl. Instrum. Meth.

Defects and glassy dynamics in solid He-4: Perspectives and current status

We review the anomalous behavior of solid He-4 at low temperatures with particular attention to the role of structural defects present in solid. The discussion centers around the possible role of two level systems and structural glassy components for inducing the observed anomalies. We propose that the origin of glassy behavior is due to the dynamics of defects like dislocations formed in He-4. Within the developed framework of glassy components in a solid, we give a summary of the results and predictions for the effects that cover the mechanical, thermodynamic, viscoelastic, and electro-elastic contributions of the glassy response of solid He-4. Our proposed glass model for solid He-4 has several implications: (1) The anomalous properties of He-4 can be accounted for by allowing defects to freeze out at lowest temperatures. The dynamics of solid He-4 is governed by glasslike (glassy) relaxation processes and the distribution of relaxation times varies significantly between different torsional oscillator, shear modulus, and dielectric function experiments. (2) Any defect freeze-out will be accompanied by thermodynamic signatures consistent with entropy contributions from defects. It follows that such entropy contribution is much smaller than the required superfluid fraction, yet it is sufficient to account for excess entropy at lowest temperatures. (3) We predict a Cole-Cole type relation between the real and imaginary part of the response functions for rotational and planar shear that is occurring due to the dynamics of defects. Similar results apply for other response functions. (4) Using the framework of glassy dynamics, we predict low-frequency yet to be measured electro-elastic features in defect rich He-4 crystals. These predictions allow one to directly test the ideas and very presence of glassy contributions in He-4.Comment: 33 pages, 13 figure

Mass estimates from optical modelling of the new TRAPUM redback PSR J1910−5320

Spider pulsars continue to provide promising candidates for neutron star mass measurements. Here we present the discovery of PSR J1910−5320, a new millisecond pulsar discovered in a MeerKAT observation of an unidentified Fermi-LAT gamma-ray source. This pulsar is coincident with a recently identified candidate redback binary, independently discovered through its periodic optical flux and radial velocity. New multicolour optical light curves obtained with ULTRACAM/New Technology Telescope in combination with MeerKAT timing and updated SOAR/Goodman spectroscopic radial velocity measurements allow a mass constraint for PSR J1910−5320. ICARUS optical light curve modelling, with streamlined radial velocity fitting, constrains the orbital inclination and companion velocity, unlocking the binary mass function given the precise radio ephemeris. Our modelling aims to unite the photometric and spectroscopic measurements available by fitting each simultaneously to the same underlying physical model, ensuring self-consistency. This targets centre-of-light radial velocity corrections necessitated by the irradiation endemic to spider systems. Depending on the gravity darkening prescription used, we find a moderate neutron star mass of either 1.6 ± 0.2 or 1.4 ± 0.2 M⊙. The companion mass of either 0.45 ± 0.04 or M⊙ also further confirms PSR J1910−5320 as an irradiated redback spider pulsar