Estimation of intrinsic and reflex contributions to muscle dynamics: a modeling study

This work evaluated system identification-based approaches for estimating stretch reflex contributions to muscle dynamics. Skeletal muscle resists externally imposed stretches via both intrinsic stiffness properties of the muscle and reflexively mediated changes in muscle activation. To separately estimate these intrinsic and reflex components, system identification approaches must make several assumptions. We examined the impact of making specific structural assumptions about the intrinsic and reflex systems on the system identification accuracy. In particular, we compared an approach that made specific parametric assumptions about the reflex and intrinsic subsystems to another that assumed more general nonparametric subsystems. A simulation-based approach was used so that the "true" characters of the intrinsic and reflex systems were known; the identification methods were judged on their abilities to retrieve these known system properties. Identification algorithms were tested on three experimentally based models describing the stretch reflex system. Results indicated that the assumed form of the intrinsic and reflex systems had a significant impact on the stiffness separation accuracy. In general, the algorithm incorporating nonparametric subsystems was more robust than the fully parametric algorithm because it had a more general structure and because it provided a better indication of the appropriateness of the assumed structure.     

The SCC BJT: a high-performance bipolar transistor compatible withhigh-density deep-submicrometer BiCMOS SRAM technologies

We present the process development and device characterization of the Selectively Compensated Collector (SCC) BJT specifically designed for high-density deep-submicrometer BiCMOS SRAM technologies. This double-poly BJT takes advantage of the self-aligned polysilicon layers of the SRAM bit cell to obtain high performance without adding excessive process complexity. Furthermore, although an NPN device, the SCC BJT is formed in a lightly doped p-well in which the collector is formed with a single 370 keV phosphorus implant to minimize parasitic junction capacitances without the use of trench isolation or recessed oxides. The suitability of this bipolar structure outside of its original FSRAM intent is proven with its potential for bipolar logic and mixed-mode RF applications. ECL delays of 50 ps at 200 μA and a CML power-delay product of 4.5 fJ at 1.1 V supply were obtained. A 900 MHz noise figure as low as 0.54 dB at 0.5 mA with an associated gain of 14.7 dB was demonstrated as well as a dual modulus ÷4/5 prescaler operating up to 3.3 GHz for a switch current of 200 μA     

Relating the N-shaped polarization curve of a PEM fuel cell to local oxygen starvation and hydrogen evolution

In this study, we experimentally investigate the appearance of a local negative differential resistance (N-NDR) branch in polarization curves of a segmented 7 by 7 cell measured under the steady and highly-dynamic conditions. Under both conditions, a comma shaped polarization curve, corresponding to depletion of oxygen, was followed by an increase in current as the cell voltage was lowered. This characteristic was measured under potentiostatic mode, where no current is forced through the cell, and at a positive cell voltage (<100 mV in steady-state and ∼300 mV in dynamic condition). With a theoretical model, we show that at these positive cell voltages and upon the depletion of oxygen, a shift in the Nernst potential occurs allowing for the hydrogen evolution reaction to take place in the cathode catalyst layer. The results of the model are complemented with experimental measurements of produced hydrogen at the cathode outlet.     

Operative management of adrenal metastases from lung carcinoma

Most surgeons consider patients with solitary adrenal metastasis from a primary lung carcinoma incurable and avoid excision of both the adrenal and primary lung tumors. However, several cases of successful surgical management of these patients recently have been reported. We reviewed 12 surgically treated patients with isolated adrenal and lung disease and identified 2 survivors of greater than fifteen years (17%) and 4 additional patients who are still alive following combined resection (34%). This survival rate, albeit in a selected population, represents an improvement over the natural history of nine months' survival. We suggest that if after six to twelve months of following patients with lung cancer and isolated adrenal metastasis no other evidence of spread of disease is evident, the tumor biology may be favorable and resection of both adrenal and lung lesions is reasonable.     

Co-optimization of the metal gate/high-k stack to achieve high-field mobility >90% of SiO/sub 2/ universal mobility with an EOT=/spl sim/1 nm

HfO/sub 2/ and HfSiON gate dielectrics with high-field electron mobility greater than 90% of the SiO/sub 2/ universal mobility and equivalent oxide thickness (EOT) approaching 1 nm are successfully achieved by co-optimizing the metal gate/high-k/bottom interface stack. Besides the thickness of the high-/spl kappa/ dielectrics, the thickness of the ALD TiN metal gate and the formation of the bottom interface also play an important role in scaling EOT and achieving high electron mobility. A phase transformation is observed for aggressively scaled HfO/sub 2/ and HfSiON, which may be responsible for the high mobility and low charge trapping of the optimized HfO/sub 2/ gate stack.     

Agonist and antagonist-dependent internalization of the human vasopressin V2 receptor

In this report we demonstrate that in HEK293 cells stably expressing the human V2 vasopressin receptor, ligand-induced internalization of the hormone receptor occurs via the clathrin-dependent pathway. Studies of receptor trafficking either by direct visualization of the V2 receptor by confocal microscopy or binding experiments show a rapid internalization (half-time 6-7 min). Blocking of the clathrin-dependent pathway by hypertonic sucrose increased vasopressin-induced cellular cAMP production and decreased the desensitization of the V2 receptor-adenylyl cyclase system. Thus, internalization appears to be a major regulatory mechanism terminating vasopressin action in HEK293 cells. Two antagonists of the vasopressin V2 receptor exerted different effects on receptor internalization, as determined by confocal fluorescence microscopy. The nonpeptidic antagonist OPC31260 did not induce any visible receptor internalization, whereas the peptidic antagonist d(CH2)5[D-Tyr(Et)2,Val4,Lys8,Tyr-NH29]VP induced a slow but substantial receptor internalization. These results suggest that long-term treatment with peptidic V2 receptor antagonists might lead to desensitization.     

Avoiding the road less traveled: how the topology of enzyme-substrate complexes can dictate product selection

Enzymes are remarkable not only in their ability to enhance reaction rates, but also because they do so selectively, directing reactive intermediates toward only one of multiple potential products. 1-Aminocyclopropane-1-carboxylate (ACC) synthase and 7,8-diaminopelargonic acid synthase are pyridoxal 5'-phosphate-dependent enzymes that utilize S-adenosyl-l-methionine as a substrate but yield different products. The former produces ACC by alpha,gamma-elimination, while the latter makes S-adenosyl-4-methylthio-2-oxobutanoate by transamination. The mechanisms of these two reactions are the same up to the formation of a quinonoid intermediate, from which they diverge. This Account explores how the active-site topology of the enzyme-intermediate complexes decides this pathway bifurcation.     

Recessed polysilicon encapsulated local oxidation

Local oxidation of silicon (LOCOS) is the most commonly used isolation technology in silicon integrated circuits. The inherently large field oxide encroachment associated with LOCOS severely limits scalability. Recessed polysilicon encapsulated local oxidation (recessed PELOX) is demonstrated to achieve both low encroachment and increased field oxide recess. These benefits are obtained without sacrificing process simplicity or defectivity as evidenced by excellent gate oxide and diode quality