Microwave and millimeter-wave power generation in silicon carbide (SiC) IMPATT devices

There are two points that should be noted. First, in the thermal resistance calculations it is assumed that the device is operating at 773 K while the results of the room temperature simulations are used. This was done because there is not enough information to correctly predict the material parameters at 773 K. Since, in general, device performance degrades with increasing temperature, the cw results are perhaps a bit optimistic. Second, the electric field in these structures gets extremely high and there might be some possibility of tunneling. This was not incorporated into the simulation. Again, this could result in different device operating conditions

Switching speeds in double‐barrier resonant‐tunneling diode structures

Switching speeds are calculated for GaAs‐AlGaAs resonant‐tunneling diode structures with different barrier widths from the time‐dependent Schrödinger equation. The speed is determined by monitoring the device current as the bias voltage is instantaneously switched. Effective mass discontinuities at the barrier and quantum well edges are included. Comparisons with previously published results using the wave packet approach are given. It is found that the turn‐off transient is dominated by the lifetime of the quasibound state; however, care must be used in calculating the lifetime.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70991/2/JAPIAU-70-12-7638-1.pd

Effect of spatially variable effective mass on static and dynamic properties of resonant tunneling devices

The effect of incorporating a spatially variable effective mass in the Schrödinger equation method of resonant tunneling device modeling is investigated. It is shown that inclusion of this effect can produce an order of magnitude difference in the calculated peak current density of the static current voltage (I‐V) curve for the resonant tunneling diode. Results for a particular In0.53Ga0.47As‐AlAs structure show that much better agreement between theory and experiment is obtained by including this effect. Also, comparison of transient results for an In0.53Ga0.47As‐In0.52Al0.48As structure shows a significant change in the diode switching transients.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69977/2/APPLAB-55-25-2631-1.pd

Effect of spacer layer thickness on the static characteristics of resonant tunneling diodes

A self‐consistent quantum mechanical simulation is used to study the effect of spacer layer thickness on such resonant tunneling diode properties as the peak current and peak‐to‐valley current ratio. It is found that with a low cathode doping the peak current is insensitive to the commonly used spacer layer thickness. However, for higher cathode doping the peak current decreases with increasing spacer layer thickness. This phenomenon is explained on the basis of the junction potential between the heavily doped cathode contact region and the undoped double‐barrier region. Thus, for device applications where a high current density is desired the cathode spacer layer should be designed as thin as possible.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70349/2/APPLAB-57-9-899-1.pd

Differences in Evaluating Fall Risk by Primary Care Provider Type

This study assessed differences in clinical fall risk assessment of older adults (65+) and clinical resources used by primary care providers (PCP). We used Porter Novelli\u27s 2016 DocStyles survey to examine clinical behavior data from PCPs (n=1128). Compared to other practitioners, nurse practitioners (NP) reported a higher percentage of their patients were older adults. The majority of NPs reported screening for falls risk routinely, but most did not use standardized fall-risk assessments to assess risk factors. There were also differences in the types of clinical resources used by NPs and other PCPs to evaluate the safety profile of medications

A self‐consistent model of Γ‐X mixing in GaAs/AlAs/GaAs quantum well structures using the quantum transmitting boundary method

We present a numerical study of the Γ‐X mixing in GaAs/AlAs/GaAs quantum well structures. A Γ‐X mixing model proposed by Liu [Appl. Phys. Lett. 51, 1019 (1987)] is extended to include the effects of self‐consistency and nonzero transverse momentum. In the present model, the coupled Schrödinger equations for Γ and X electron envelope wave functions are solved self‐consistently with Poisson’s equation to calculate the electron transmission probability and wave functions, which lead to the current‐voltage (I‐V) characteristics of single barrier and double barrier resonant tunneling diode structures. The quantum transmitting boundary method is employed in the model for numerical solution of the coupled Schrödinger equations, which proves to be very stable and efficient, even for large (≳2000 Å) structures. The features of Γ‐X mixing, such as the resonance/antiresonance in the transmission probability and the virtual bound states, are clearly demonstrated. Additional physical features are observed in the transmission probability and the wave functions under applied bias conditions. Our work shows that inclusion of transverse momentum, variable effective mass, and the self‐consistent potential is important in the realistic modeling of I‐V characteristics for structures exhibiting Γ‐X coupling.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69686/2/JAPIAU-74-8-5053-1.pd

Brown· Midrib Sorghum Silage for Midlactation Dairy Cows

Brown midrib sorghum silage was compared with alfalfa, corn, and normal sorghum silages for its effect on performance, ruminal metabolism, and digestive kinetics of Holstein dairy cows in midlactation. Twelve cows averaging 90 ± 5 DIM were assigned to one of four diets in replicated 4 X 4 Latin squares with 4-wk periods. Additionally, 3 ruminally fistulated cows (95 ± 20 DIM) were assigned to the same diets in a 3x 4 Youden square for measurement of ruminal characteristics. Diets were fed as isonitrogenous TMR that contained 65% silage (OM basis). The DMl was greater for the corn and brown midrib sorghum (4% of BW/d) than for the alfalfa and normal sorghum diets (3.4% of BW/d). The brown midrib sorghum supported FCM production that was similar to that of cows on corn and alfalfa diets (25.8 kg/d), but cows fed normal sorghum produced less milk and fewer milk components. Source of silage had no effect on eating time, but rumination was least for the alfalfa.diet.. Ruminal pH and ammonia concentrations were similar for all diets. Total VFA concentrations were greatest for the corn and brown midrib sorghum diets. The brown midrib sorghum had greater in situ extent of ruminal NDF digestion than did the normal sorghum, which agreed with in vitro data. The brown midrib sorghum used in this experiment supported FCM production similar to the corn and alfalfa silages commonly fed to dairy cows in midlactation

Brown· Midrib Sorghum Silage for Midlactation Dairy Cows

Brown midrib sorghum silage was compared with alfalfa, corn, and normal sorghum silages for its effect on performance, ruminal metabolism, and digestive kinetics of Holstein dairy cows in midlactation. Twelve cows averaging 90 ± 5 DIM were assigned to one of four diets in replicated 4 X 4 Latin squares with 4-wk periods. Additionally, 3 ruminally fistulated cows (95 ± 20 DIM) were assigned to the same diets in a 3x 4 Youden square for measurement of ruminal characteristics. Diets were fed as isonitrogenous TMR that contained 65% silage (OM basis). The DMl was greater for the corn and brown midrib sorghum (4% of BW/d) than for the alfalfa and normal sorghum diets (3.4% of BW/d). The brown midrib sorghum supported FCM production that was similar to that of cows on corn and alfalfa diets (25.8 kg/d), but cows fed normal sorghum produced less milk and fewer milk components. Source of silage had no effect on eating time, but rumination was least for the alfalfa.diet.. Ruminal pH and ammonia concentrations were similar for all diets. Total VFA concentrations were greatest for the corn and brown midrib sorghum diets. The brown midrib sorghum had greater in situ extent of ruminal NDF digestion than did the normal sorghum, which agreed with in vitro data. The brown midrib sorghum used in this experiment supported FCM production similar to the corn and alfalfa silages commonly fed to dairy cows in midlactation

Dynamin-related protein 1 is required for normal mitochondrial bioenergetic and synaptic function in CA1 hippocampal neurons.

Disrupting particular mitochondrial fission and fusion proteins leads to the death of specific neuronal populations; however, the normal functions of mitochondrial fission in neurons are poorly understood, especially in vivo, which limits the understanding of mitochondrial changes in disease. Altered activity of the central mitochondrial fission protein dynamin-related protein 1 (Drp1) may contribute to the pathophysiology of several neurologic diseases. To study Drp1 in a neuronal population affected by Alzheimer's disease (AD), stroke, and seizure disorders, we postnatally deleted Drp1 from CA1 and other forebrain neurons in mice (CamKII-Cre, Drp1lox/lox (Drp1cKO)). Although most CA1 neurons survived for more than 1 year, their synaptic transmission was impaired, and Drp1cKO mice had impaired memory. In Drp1cKO cell bodies, we observed marked mitochondrial swelling but no change in the number of mitochondria in individual synaptic terminals. Using ATP FRET sensors, we found that cultured neurons lacking Drp1 (Drp1KO) could not maintain normal levels of mitochondrial-derived ATP when energy consumption was increased by neural activity. These deficits occurred specifically at the nerve terminal, but not the cell body, and were sufficient to impair synaptic vesicle cycling. Although Drp1KO increased the distance between axonal mitochondria, mitochondrial-derived ATP still decreased similarly in Drp1KO boutons with and without mitochondria. This indicates that mitochondrial-derived ATP is rapidly dispersed in Drp1KO axons, and that the deficits in axonal bioenergetics and function are not caused by regional energy gradients. Instead, loss of Drp1 compromises the intrinsic bioenergetic function of axonal mitochondria, thus revealing a mechanism by which disrupting mitochondrial dynamics can cause dysfunction of axons

Continuous Uniform Finite Time Stabilization of Planar Controllable Systems

Continuous homogeneous controllers are utilized in a full state feedback setting for the uniform finite time stabilization of a perturbed double integrator in the presence of uniformly decaying piecewise continuous disturbances. Semiglobal strong $\mathcal{C}^1$ Lyapunov functions are identified to establish uniform asymptotic stability of the closed-loop planar system. Uniform finite time stability is then proved by extending the homogeneity principle of discontinuous systems to the continuous case with uniformly decaying piecewise continuous nonhomogeneous disturbances. A finite upper bound on the settling time is also computed. The results extend the existing literature on homogeneity and finite time stability by both presenting uniform finite time stabilization and dealing with a broader class of nonhomogeneous disturbances for planar controllable systems while also proposing a new class of homogeneous continuous controllers