Fabrication of integrated planar gunn diode and micro-cooler on GaAs substrate

We demonstrate fabrication of an integrated micro cooler with the planar Gunn diode and characterise its performance. First experimental results have shown a small cooling at the surface of the micro cooler. This is first demonstration of an integrated micro-cooler with a planar Gunn diode

Micro-cooler Enhancements by Barrier Interface Analysis

Peer reviewedPublisher PD

Impact ionisation electroluminescence in planar GaAs-based heterostructure Gunn diodes:Spatial distribution and impact of doping nonuniformities

When biased in the negative differential resistance regime, electroluminescence (EL) is emitted from planar GaAs heterostructure Gunn diodes. This EL is due to the recombination of electrons in the device channel with holes that are generated by impact ionisation when the Gunn domains reach the anode edge. The EL forms non-uniform patterns whose intensity shows short-range intensity variations in the direction parallel to the contacts and decreases along the device channel towards the cathode. This paper employs Monte Carlo models, in conjunction with the experimental data, to analyse these non-uniform EL patterns and to study the carrier dynamics responsible for them. It is found that the short-range lateral (i.e., parallel to the device contacts) EL patterns are probably due to non-uniformities in the doping of the anode contact, illustrating the usefulness of EL analysis on the detection of such inhomogeneities. The overall decreasing EL intensity towards the anode is also discussed in terms of the interaction of holes with the time-dependent electric field due to the transit of the Gunn domains. Due to their lower relative mobility and the low electric field outside of the Gunn domain, freshly generated holes remain close to the anode until the arrival of a new domain accelerates them towards the cathode. When the average over the transit of several Gunn domains is considered, this results in a higher hole density, and hence a higher EL intensity, next to the anode

Vegetated Filter Strip Removal of Cattle Manure Constituents in Runoff

Pasture runoff can contribute to elevated concentrations of nutrients, solids, and bacteria in downstream waters. The objective of this study was to determine the effects of vegetative filter strip (VFS) length on concentrations and transport of nitrogen, phosphorus, solids and fecal coliform in runoff from plots treated with cattle manure. Three plots with dimensions of 2.4 × 30.5 m were used. The upper 12.2 m of each plot was treated with cattle manure, while the lower 18.3 m acted as a VFS. Runoff produced by rainfall simulators was sampled at VFS lengths of 0, 6.1, 12.2, and 18.3 m and analyzed for total Kjeldahl nitrogen (N), ammonia N, nitrate N, total phosphorus (P), ortho-P, fecal coliforms, total suspended solids and other parameters. The VFS significantly reduced concentrations and mass transport of incoming solids, fecal coliform, and most nutrient forms, particularly P. The relationships among VFS length, concentration and mass transport were well-represented by first-order exponential decay functions. Approximately 75% of incoming total Kjeldahl N, total P, ortho-P, and total suspended solids was removed within the first 6.1 m of the filter strips. Runoff concentrations of fecal coliform concentrations entering the filter strips were as high as 2 × 107 FC/100 mL; after a filter length of 6.1 m, however, the runoff exhibited no measurable concentration of fecal coliforms. This experiment suggests that even relatively short filter strips can markedly improve quality of runoff from grassed areas receiving cattle manure

Role of Smad4 on TGF-β–induced extracellular matrix stimulation in mesangial cells

Role of Smad4 on TGF-β–induced extracellular matrix stimulation in mesangial cells.BackgroundThe best characterized signaling pathway employed by transforming growth factor-β (TGF-β) is the Smad pathway; however, its role in matrix production in mesangial cells is unclear. We focused on Smad4, as Smad4 is essential for the activation of Smad-dependent target genes.MethodsTo investigate the function of Smad4 in extracellular matrix (ECM) production, we generated several stably transfected mesangial cell lines (MMC) that have a deletion in the linker region (Smad4ΔM4: Δ275-322) or have a deletion in MH1 of Smad4 (Smad4N4: Δ1-136). The ECM genes, α1 type I collagen (COL1A1), plasminogen activator inhibitor-1 (PAI-1) and fibronectin (FN) were assessed in wild-type mesangial cells and stably transfected Smad4-DN cell lines in the absence and presence of TGF-β.ResultsAs compared to wild-type MMC that had a 10.8-fold stimulation of TGF-β–induced p3TP-Lux activity, MMC stably transfected with Smad4ΔM4 and Smad4N4 had only a 2.0-fold and 1.3-fold stimulation, respectively, indicating that they had dominant-negative effects on TGF-β signaling. Basal and TGF-β–induced COL1A1 expression in Smad4 dominant-negative cells were dramatically reduced to very low levels. The early (2 hours) TGF-β–induced PAI-1 mRNA expression was inhibited; however, the sustained (24 to 48 hours) TGF-β–induced expression was not affected in Smad4 dominant-negative cells. For FN, TGF-β–induced expression was maintained in Smad4-dominant negative cells.ConclusionThese results indicate that Smad4 is essential for basal and TGF-β–induced COL1A1 expression, and contributes to the early, but not sustained TGF-β–induced PAI-1 expression in mesangial cells. However, TGF-β–induced FN expression is independent of Smad4. In conclusion, Smad4 has a discriminate effect in mediating specific ECM molecules stimulated by TGF-β in mesangial cells

Observation of ultrafast internal conversion in fullerene anions in solution

The ultrafast decay rates of photoexcited View the MathML source ions have been measured in the condensed phase. The mechanism for decay is internal conversion, and the decay rate is a strong function of the charge on the ion. A bottleneck in the ground state recovery has also been detected, and its interpretation is discussed

Stocking System Effects on Soil and Forage Characteristics, and Performance of Fall-Calving Cows Grazing Cool-Season Grass Pastures (A Progress Report)

The effects of stocking densities of fall-calving Angus cattle grazing cool-season pastures on cow and calf performance; forage mass, quality, and botanical composition; soil carbon content and compaction; and grazing selectivity of cattle were evaluated. Two blocks of three 10-acre cool-season pastures, divided into 1-acre paddocks, were grazed by 10 fall-calving Angus cows by one of three stocking systems: rotational stocking (RS, low stocking density), strip stocking (SS, moderate stocking density), and mob stocking (MS, high stocking density). Pastures were grazed from mid-May through late September in 2010 (yr 1) and 2011 (yr 2). Cattle received a daily live forage dry matter (DM) allowance of 4.0 and 3.2% of cow body weight (BW) in yr 1 and 2, respectively. Cattle in RS pastures were moved to new paddocks after initial forage sward height, measured with a falling plate meter (8.8 lb/yd2), was reduced by 50% by measurement (yr 1), and after the estimated intake at 3.2% of cow BW/day (yr 2). Cattle in SS and MS pastures received strips containing 100 and 25% of the daily forage allowance one and four times per day, respectively. Cow BCS did not differ between treatments in any month of either year. Cow BW was greater in MS than RS and SS pastures in June of yr 2 and greater in RS than MS pastures in August of yr 2, but did not differ in any other months of either year. Birth weight and average daily gain (ADG) of live calves at the end of the trial did not differ between treatments in either year; however, there were fewer calves per cow in MS pastures at the termination of the trial in yr 2. Forage sward height did not differ between treatments in any month of either year. Rotational stocking decreased forage disappearance in yr 2 compared to strip or mob stocking. Forage disappearance was lower in RS than SS and MS pastures in May and June of both years and was greater in RS than SS pastures in September of yr 1, but did not differ in any other months. Forage botanical composition prior to grazing each year did not differ between years, but dead forage as a percent of total forage DM was lower in RS than SS and MS pastures in yr 2. Soil bulk density from 0-3 inches in yr 1, water infiltration rate into the soil in either year, and penetration resistance at depths of 0 and 3 inches in yr 2, did not differ between treatments in any month. Soil penetration resistance at 6 inches was greater in SS than RS and MS pastures in May, and was greater in MS than SS pastures in August. Grazing selectivity did not differ between treatments in yr 1. Results suggest that, at constant forage allocation, mob stocking does not affect cow or live calf performance, but may reduce the proportion of surviving calves. Mob stocking also does not affect forage mass, botanical composition, or soil compaction measures within the first two years of implementation

Mortality among residents of shelters, rooming houses, and hotels in Canada: 11 year follow-up study

Objective To examine mortality in a representative nationwide sample of homeless and marginally housed people living in shelters, rooming houses, and hotels

A critical role for cystathionine-β-synthase in hydrogen sulfide-mediated hypoxic relaxation of the coronary artery

Hypoxia-induced coronary artery vasodilatation protects the heart by increasing blood flow under ischemic conditions, however its mechanism is not fully elucidated. Hydrogen sulfide (H2S) is reported to be an oxygen sensor/transducer in the vasculature. The present study aimed to identify and characterise the role of H2S in the hypoxic response of the coronary artery, and to define the H2S synthetic enzymes involved. Immunoblotting and immunohistochemistry showed expression of all three H2S-producing enzymes, cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (MPST), in porcine coronary artery. Artery segments were mounted for isometric tension recording; hypoxia caused a transient endothelium-dependent contraction followed by prolonged endothelium-independent relaxation. The CBS inhibitor amino-oxyacetate (AOAA) reduced both phases of the hypoxic response. The CSE inhibitor dl-propargylglycine (PPG) and aspartate (limits MPST) had no effect alone, but when applied together with AOAA the hypoxic relaxation response was further reduced. Exogenous H2S (Na2S and NaHS) produced concentration-dependent contraction followed by prolonged relaxation. Responses to both hypoxia and exogenous H2S were dependent on the endothelium, NO, cGMP, K+ channels and Cl−/HCO3 − exchange. H2S production in coronary arteries was blocked by CBS inhibition (AOAA), but not by CSE inhibition (PPG). These data show that H2S is an endogenous mediator of the hypoxic response in coronary arteries. Of the three H2S-producing enzymes, CBS, expressed in the vascular smooth muscle, appears to be the most important for H2S generated during hypoxic relaxation of the coronary artery. A contribution from other H2S-producing enzymes only becomes apparent when CBS activity is inhibited

Terahertz oscillations in an In_0.53Ga_0.47As submicron planar gunn diode

The length of the transit region of a Gunn diode determines the natural frequency at which it operates in fundamental mode – the shorter the device, the higher the frequency of operation. The long-held view on Gunn diode design is that for a functioning device the minimum length of the transit region is about 1.5μm, limiting the devices to fundamental mode operation at frequencies of roughly 60 GHz. Study of these devices by more advanced Monte Carlo techniques that simulate the ballistic transport and electron-phonon interactions that govern device behaviour, offers a new lower bound of 0.5μm, which is already being approached by the experimental evidence that has shown planar and vertical devices exhibiting Gunn operation at 600nm and 700nm, respectively. The paper presents results of the first ever THz submicron planar Gunn diode fabricated in In<sub>0.53</sub>Ga<sub>0.47</sub>A on an InP substrate, operating at a fundamental frequency above 300 GHz. Experimentally measured rf power of 28 µW was obtained from a 600 nm long ×120 µm wide device. At this new length, operation in fundamental mode at much higher frequencies becomes possible – the Monte Carlo model used predicts power output at frequencies over 300 GHz