Microwave backscatter modeling of erg surfaces in the Sahara Desert

The Sahara Desert includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. Previous study shows that Saharan ergs exhibit significant radar backscatter (σ°) modulation with azimuth angle (f). We use σ° measurements observed at various incidence angles and f from the NASA Scatterometer (NSCAT), the SeaWinds scatterometer, the ERS scatterometer (ESCAT), and the Tropical Rainfall Measuring Mission\u27s Precipitation Radar to model the σ° response from sand dunes. Observations reveal a characteristic relationship between the backscatter modulation and the dune type, i.e., the number and orientation of the dune slopes. Sand dunes are modeled as a composite of tilted rough facets, which are characterized by a probability distribution of tilt with a mean value, and small ripples on the facet surface. The small ripples are modeled as cosinusoidal surface waves that contribute to the return signal at Bragg angles only. Longitudinal and transverse dunes are modeled with rough facets having Gaussian tilt distributions. The model results in a σ° response similar to NSCAT and ESCAT observations over areas of known dune types in the Sahara. The response is high at look angles equal to the mean tilts of the rough facets and is lower elsewhere. This analysis provides a unique insight into scattering by large-scale sand bedforms

Modeling microwave emissions of erg surfaces in the Sahara Desert

Sand seas (ergs) of the Sahara are the most dynamic parts of the desert. Aeolian erosion, transportation, and deposition continue to reshape the surface of the ergs. The large-scale features (dunes) of these bedforms reflect the characteristics of the sand and the long-term wind. Radiometric emissions from the ergs have strong dependence on the surface geometry. We model the erg surface as composed of tilted rough facets. Each facet is characterized by a tilt distribution dependent upon the surface roughness of the facet. The radiometric temperature (T(b)) of ergs is then the weighted sum of the T(b) from all the facets. We use dual-polarization T(b) measurements at 19 and 37 GHz from the Special Sensor Microwave Imager aboard the Defense Meteorological Satellite Program and the Tropical Rainfall Measuring Mission Microwave Imager to analyze the radiometric response of erg surfaces and compare them to the model results. The azimuth angle (φ) modulation of T(b) is caused by the surface geometrical characteristics. It is found that longitudinal and transverse dune fields are differentiable based on their polarization difference (ΔT(b)) φ-modulation, which reflects type and orientation of dune facets. ΔT(b) measurements at 19 and 37 GHz provide consistent results. The magnitude of ΔT(b) at 37 GHz is lower than at 19 GHz due to higher attenuation. The analysis of ΔT(b) over dry sand provides a unique insight into radiometric emission over ergs

Quantum spin liquid in a kagome lattice spin-1/2 XY model with four-site exchange

We study the ground state phase diagram of a two-dimensional kagome lattice spin-1/2 XY model (J) with a four-site ring exchange interaction (K) using quantum Monte Carlo simulations. We find that the superfluid phase, existing in the regime of small ring exchange, undergoes a direct transition to a Z_2 quantum spin liquid phase at (K/J)_c ~ 22, which is related to the phase proposed by Balents, Girvin and Fisher [Phys. Rev. B, 65 224412 (2002)]. The quantum phase transition between the superfluid and the spin liquid phase has exponents z and \nu falling in the 3D XY universality class, making it a candidate for an exotic XY* quantum critical point, mediated by the condensation of bosonic spinons.Comment: 4 pages, 5 figure

Phase 1 study of sirolimus in combination with oral cyclophosphamide and topotecan in children and young adults with relapsed and refractory solid tumors.

PurposeTo determine the maximum tolerated dose (MTD), toxicities, and pharmacodynamics effects of sirolimus combined with oral metronomic topotecan and cyclophosphamide in a pediatric population.Materials and methodsPatients who were 1 to 30 years of age with relapsed/refractory solid tumors (including CNS) were eligible. Patients received daily oral sirolimus and cyclophosphamide (25-50 mg/m2/dose) on days 1-21 and oral topotecan (0.8 mg/m2/dose) on days 1-14 in 28-day cycles. Sirolimus steady-state plasma trough concentrations of 3-7.9 ng/mL and 8-12.0 ng/mL were evaluated, with dose escalation based on a 3+3 phase 1 design. Biomarkers of angiogenesis were also evaluated.ResultsTwenty-one patients were treated (median age 18 years; range 9-30). Dose-limiting toxicities included myelosuppression, ALT elevation, stomatitis, and hypertriglyceridemia. The MTD was sirolimus with trough goal of 8-12.0 ng/mL; cyclophosphamide 25 mg/m2/dose; and topotecan 0.8 mg/m2/dose. No objective responses were observed. Four patients had prolonged stable disease > 4 cycles (range 4-12). Correlative biomarker analyses demonstrated reductions in thrombospondin-1 (p=0.043) and soluble vascular endothelial growth factor receptor-2 plasma concentrations at 21 days compared to baseline.ConclusionsThe combination of oral sirolimus, topotecan, and cyclophosphamide was well tolerated and biomarker studies demonstrated modulation of angiogenic pathways with this regimen

North Atlantic ecosystem sensitivity to Holocene shifts in Meridional Overturning Circulation

Rapid changes in North Atlantic climate over the last millennia were driven by coupled sea surface/atmospheric processes and rates of deep-water formation. Holocene climate changes, however, remain poorly documented due to a lack of high-resolution paleoclimate records, and their impacts on marine ecosystems remain unknown. We present a 4500 years absolute-dated sea surface radiocarbon record from northeast Atlantic cold-water corals. In contrast to the current view that surface ocean changes occurred on millennial-scale cycles, our record shows more abrupt changes in surface circulation. Changes were centered at 3.4, 2.7, 1.7 and 1.2 ky BP, and associated with atmospheric re-organization. Solar irradiance may have influenced these anomalies, but changes in North Atlantic deep-water convection are likely to have amplified these signals. Critically, we provide the first evidence that these perturbations in Atlantic Meridional Overturning Circulation led to the decline of cold-water coral ecosystems from 1.2 to ~ 0.1 ky BP

Lower job satisfaction among workers migrating within Europe: A gender paradox

Intra-European migrants reported lower job satisfaction levels than native workers, in three rounds of the European Social Survey. This deficit was also experienced by their descendants (the second generation), despite the latter generation achieving native levels of household income. At least some part of these lower levels of job satisfaction was associated with a clustering into lower-productivity industries. There are striking gender differences in experiences: among men the first generation is just as likely to be satisfied with their jobs as the ‘native’ population, whilst it is the second generation who are less likely to achieve job satisfaction. For women, both generations experienced a deficit in job satisfaction. This may reflect changing expectations of work among men, and integration for women, across generations, and contrasts with the convergence in earnings over time. The country of origin, within Europe, did not seem to be associated with levels of job satisfaction

Neutrophil-derived microvesicle induced dysfunction of brain microvascular endothelial cells in vitro

The blood-brain barrier (BBB), composed of brain microvascular endothelial cells (BMEC) that are tightly linked by tight junction (TJ) proteins, restricts the movement of molecules between the periphery and the central nervous system. Elevated systemic levels of neutrophils have been detected in patients with altered BBB function, but the role of neutrophils in BMEC dysfunction is unknown. Neutrophils are key players of the immune response and, when activated, produce neutrophil-derived microvesicles (NMV). NMV have been shown to impact the integrity of endothelial cells throughout the body and we hypothesize that NMV released from circulating neutrophils interact with BMEC and induce endothelial cell dysfunction. Therefore, the current study investigated the interaction of NMV with human BMEC and determined whether they altered gene expression and function in vitro. Using flow cytometry and confocal imaging, NMV were shown to be internalized by the human cerebral microvascular endothelial cell line hCMEC/D3 via a variety of energy-dependent mechanisms, including endocytosis and macropinocytosis. The internalization of NMV significantly altered the transcriptomic profile of hCMEC/D3, specifically inducing the dysregulation of genes associated with TJ, ubiquitin-mediated proteolysis and vesicular transport. Functional studies confirmed NMV significantly increased permeability and decreased the transendothelial electrical resistance (TEER) of a confluent monolayer of hCMEC/D3. These findings indicate that NMV interact with and affect gene expression of BMEC as well as impacting their integrity. We conclude that NMV may play an important role in modulating the permeability of BBB during an infection

Guard-cell-targeted overexpression of Arabidopsis \u3ci\u3eHexokinase 1\u3c/i\u3e can improve water use efficiency in field-grown tobacco plants

Water deficit currently acts as one of the largest limiting factors for agricultural productivity worldwide. Additionally, limitation by water scarcity is projected to continue in the future with the further onset of effects of global climate change. As a result, it is critical to develop or breed for crops that have increased water use efficiency and that are more capable of coping with water scarce conditions. However, increased intrinsic water use efficiency (iWUE) typically brings a trade-off with CO2 assimilation as all gas exchange is mediated by stomata, through which CO2 enters the leaf while water vapor exits. Previously, promising results were shown using guard-cell-targeted overexpression of hexokinase to increase iWUE without incurring a penalty in photosynthetic rates or biomass production. Here, two homozygous transgenic tobacco (Nicotiana tabacum) lines expressing Arabidopsis Hexokinase 1 (AtHXK1) constitutively (35SHXK2 and 35SHXK5) and a line that had guard-cell-targeted overexpression of AtHXK1 (GCHXK2) were evaluated relative to wild type for traits related to photosynthesis and yield. In this study, iWUE was significantly higher in GCHXK2 compared with wild type without negatively impacting CO2 assimilation, although results were dependent upon leaf age and proximity of precipitation event to gas exchange measurement