Analysis of a cross wedge rolling process for producing drive shafts

The paper discusses the problems of forming parts such as stepped shafts by cross wedge rolling (CWR). In industrial practice, this rolling process is performed at stages, i.e., in several passes, when large cross-sectional reductions are involved. The same can also be done using a different design of this forming process, namely, multi-wedge cross rolling (MWCR), in which the workpiece is simultaneously formed by several pairs of tools (wedges). This paper compares the above two methods with respect to forming a drive shaft. Wedge tools used in both forming processes are described, and the numerical results of the simulations performed to verify the adopted solutions are reported. The results demonstrate that the MWCR method offers more advantages than the classical CWR technique. Consequently, MWCR is then verified in experimental tests. The experimental results confirm that parts such as stepped shafts can be formed by the MWCR method.     

Exogenous Asymmetric Dimethylarginine (ADMA) in Pathogenesis of Ischemia-Reperfusion-Induced Gastric Lesions: Interaction with Protective Nitric Oxide (NO) and Calcitonin Gene-Related Peptide (CGRP)

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide (NO) synthesis inhibitor and pro-inflammatory factor. We investigated the role of ADMA in rat gastric mucosa compromised through 30 min of gastric ischemia (I) and 3 h of reperfusion (R). These I/R animals were pretreated with ADMA with or without the combination of l-arginine, calcitonin gene-related peptide (CGRP) or a small dose of capsaicin, all of which are known to afford protection against gastric lesions, or with a farnesoid X receptor (FXR) agonist, GW 4064, to increase the metabolism of ADMA. In the second series, ADMA was administered to capsaicin-denervated rats. The area of gastric damage was measured with planimetry, gastric blood flow (GBF) was determined by H₂-gas clearance, and plasma ADMA and CGRP levels were determined using ELISA and RIA. ADMA significantly increased I/R-induced gastric injury while significantly decreasing GBF, the luminal NO content, and the plasma level of CGRP. This effect of ADMA was significantly attenuated by pretreatment with CGRP, l-arginine, capsaicin, or a PGE₂ analogue. In GW4064 pretreated animals, the I/R injury was significantly reduced and this effect was abolished by co-treatment with ADMA. I/R damage potentiated by ADMA was exacerbated in capsaicin-denervated animals with a further reduction of CGRP. Plasma levels of IL-10 were significantly decreased while malonylodialdehyde (MDA) and plasma TNF-α contents were significantly increased by ADMA. In conclusion, ADMA aggravates I/R-induced gastric lesions due to a decrease of GBF, which is mediated by a fall in NO and CGRP release, and the enhancement of lipid peroxidation and its pro-inflammatory properties.     

The Influence of Si/Al Ratio on the Distribution of OH Groups in Zeolites with MWW Topology

A series of MWW-type zeolites of increasing Si/Al ratio were investigated with respect to their acidic properties. Concentration of the Brønsted acid centers located at the external crystal surface was invariant for the entire series. Ethanol conversion to ethyl-tert-butyl ether, proceeding only at the external surface, was also constant. The OH groups in MWW zeolites were found to be homogeneous with proton affinity value equal to 1142.7 kJ/mol.     

Incorporating platinum precursors into a NaA-zeolite synthesis mixture promoting the formation of nanosized zeolite

Sodium A-zeolite with different platinum contents were prepared by directly incorporating platinum precursor (Pt(NH₃)₄Cl₂) into the zeolite during synthesis. Pt/KA-zeolite was then obtained by ion-exchange with KCl solution. The effect of platinum concentration on the crystal morphology and platinum dispersion was investigated by hydrogen chemisorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), and time-of-flight secondary ion mass spectrometer (TOF-SIMS). SEM results revealed a bimodal crystal size distribution for NaA-zeolite with low platinum concentration (<1 wt%). Chamfered edges were found for all the larger cubic crystals (～4 μm). Two types of cubic crystals, smooth surface cubes with chamfered edges and rough surface cubes, were observed for the smaller crystals (～400 nm). The proportion of the rough surface nanosized cubes increased as the platinum content increased. At about 4 wt% platinum, only nanosized rough surface cubic crystals were obtained, which were transformed into nanocrystals of KF-zeolite after ion-exchange with KCl, as indicated by X-ray diffraction results. TOF-SIMS data taken before and after sputtering the surface layers revealed that platinum was distributed homogeneously inside of the zeolite, which was supported by hydrogen chemisorption results, indicating that platinum particles were confined in the zeolitic cages for both the microsized and nanosized cubic crystals. A mechanism was proposed to elucidate the role of platinum precursor on the nucleation and growth of nanosized zeolite, which is consistent with all of the characterization results.     

Partnering analytic models and dynamic secondary ion mass spectrometry simulations to interpret depth profiles due to kiloelectronvolt cluster bombardment

The analytical steady-state statistical sputtering model (SS-SSM) is utilized to interpret molecular dynamics (MD) simulations of depth profiling of Ag solids with keV cluster beams of C(60) and Au(3) under different incident energy and angle conditions. Specifically, the results of the MD simulations provide the input to the SS-SSM and the result is a depth profile of a delta layer. It has been found that the rms roughness of each system correlates with the total displacement yield, a new quantity introduced in this study that follows naturally from the SS-SSM. The results indicate that the best depth profiles occur when the displacement yield is low and the sputtering yield is high. Moreover, it is determined that the expected value of the delta layer position as calculated from a depth profile rather than the peak position in the depth profile is the best indicator of the actual delta layer position.     

Aging of complex heart rate dynamics

We reveal unexpected origins of age induced departure from 1/f-type temporal scaling in healthy human heart rate. Contrary to the widely established view, we provide evidence that age induced dynamical imbalance in the autonomic control is not due to the emergent functional dominance of the sympathetic nervous system (SNS), but due to emerging (age dependent) relative dynamic dominance of the parasympathetic nervous system function. In particular, we demonstrate that the age induced alterations of healthy heart rate dynamics asymptotically resemble those in so-called primary autonomic failure with neurogenic SNS dysfunction and in other neurodegenerative disorders, including Parkinson's disease even without known autonomic abnormalities. Based upon this, we propose a novel picture of "autonomic aging," characterized by an insufficiency of the SNS function to cope dynamically with various environmental stimuli.     

Procedure for determining maximum sustainable power generated by microbial fuel cells

Power generated by microbial fuel cells is computed as a product of current passing through an external resistor and voltage drop across this resistor. If the applied resistance is very low, then high instantaneous power generated by the cell is measured, which is not sustainable; the cell cannot deliver that much power for long periods of time. Since using small electrical resistors leads to erroneous assessment of the capabilities of microbial fuel cells, a question arises: what resistor should be used in such measurements? To address this question, we have defined the sustainable power as the steady state of power delivery by a microbial fuel cell under a given set of conditions and the maximum sustainable power as the highest sustainable power that a microbial fuel cell can deliver under a given set of conditions. Selecting the external resistance that is associated with the maximum sustainable power in a microbial fuel cell (MFC) is difficult because the operator has limited influence on the main factors that control power generation: the rate of charge transfer at the current-limiting electrode and the potential established across the fuel cell. The internal electrical resistance of microbial fuel cells varies, and it depends on the operational conditions of the fuel cell. We have designed an empirical procedure to predict the maximum sustainable power that can be generated by a microbial fuel cell operated under a given set of conditions. Following the procedure, we change the external resistors incrementally, in steps of 500 omega every 10, 60, or 180 s and measure the anode potential, the cathode potential, and the cell current. Power generated in the microbial fuel cell that we were using was limited by the anodic current. The anodic potential was used to determine the condition where the maximum sustainable power is obtained. The procedure is simple, microbial fuel cells can be characterized within an hour, and the results of the measurements can serve many purposes, such as: (1) estimating power generation in various MFCs, (2) comparing power generation in MFCs using different electroactive reactants, (3) quantifying the effects of the operational regime on the power generation in MFCs, and finally, (4) the purpose for which the procedure was designed, optimizing the performance of existing MFCs.     

A new efficient algorithm for optimal assignment of smart weapons to targets

In the modern battlefields smart weapons inherently rely on the sensors. The benefit of assigning a given weapon to a target often depends on the pre-assigned sensor. In this paper we present an efficient algorithm to optimally assign sensors and weapons to targets. This algorithm is derived from the well-known auction algorithm, and it is named as Swt-opt. We prove that Swt-opt converges to an optimal solution.     

Temperature dependence of Bi4Ge3O12 photoluminescence spectra

Bi₄Ge₃O₁₂ single crystals were obtained using Czochralski growth method. Photoluminescence spectra were analyzed versus temperature from 12 to 295 K. Besides the previously observed emission bands at 610 and 820 nm, the new emission band at 475 nm was found by a careful temperature dependence measurement in the present study. The influence of basic and defect structure on the shape and position of the spectra versus temperature was discussed.