AC Part Research Articles

Differential remodeling of carotid artery in spontaneously hypertensive and hereditary hyper-triglyceridemic rats

High blood pressure, increased level of cholesterol, diabetes, hypertriglyceridemia and obesity are risk factors accompanied metabolic syndrome. The aim of the study was to compare geometry of carotid artery (AC) of 3-week-old (3w) and 52-week-old (52w) hereditary hypertriglyceridemic rats (hHTG) and spontaneously hypertensive rats (SHR) which represent a genetic model of human essential hypertension with age-matched Wistar rats. After sacrificing the rats were perfused with a glutaraldehyde fixative under the pressure 90 mm Hg (3w) and 120 mm Hg (52w) for 10 min via cannula placed into left ventricle. Middle part of AC was excised and processed according to standard electron microscopy procedure. Geometry of AC was evaluated in light microscopy. SHR vs. Wistar rats: BP of 3w did not differ, in 52w it was increased; cardiac hypertrophy was found in both ages; wall thickness (WT) and cross sectional area (CSA) in 3w did not differ, in 52w both were increased; inner diameter (ID) in 3w and 52w was decreased; WT/ID was increased in both ages. Hereditary HTG vs. Wistar rats: BP was increased in both periods; cardiac hypertrophy was observed in 3w; WT in 3w was decreased, in 52w it was increased; CSA and ID were decreased in both ages; WT/ID was increased only in 52w. Discrepancies between development of BP, cardiac hypertrophy in SHR and hHTG rats were observed. Alterations of BP were not in harmony with alterations in geometry of carotid arteries in both SHR and hHTG rats. We suggest that BP is not the main stimuli evoked hemodynamic and structural alterations of cardiovascular system in ontogenic development of SHR and hHTG rats.

NUMERICAL CALCULATIONS OF AC RESPONSE IN AHARONOV-BOHM RINGS

We present a detailed theoretical investigation on the transport properties of the one dimensional quantum rings. The Aharonov-Bohm effects under the low-voltage and low-frequency perturbation have been carefully studied. Scattering matrix method is adopted to obtain the ac response at external perturbation. The results show that the dc and ac parts of the conductance are dependent on the incident electron energy, magnetic field strength, and the coupling parameter. Some impressive characteristics of the emittance have also been discussed.

STRAIGHT TALK ON ACADEMIC HIRING

THE PANELISTS TAKING PART IN the presidential event on academic hiring at last month's American Chemical Society national meeting in San Diego did not shy away from the tough questions. While providing practical insights into the hiring process, from drafting a compelling cover letter to schmoozing with the provost, the diverse group tackled such challenging issues as whether to identify yourself as a member of a minority group and when to bring up the complication that your spouse needs a job, too. The panel discussion, like its predecessor a year ago at the ACS national meeting in Anaheim, Calif. (C&EN, April 19, 2004, page 45), was part of ACS's ongoing Academic Employment Initiative. Championed by Immediate Past-President Charles P. Casey, the goal of AEI is to broaden the process by which chemistry faculty members are hired. Institutions tend to bring only a handful of candidates—selected largely on the basis of their paper ...

Noise-resistant area integration pulse oximetry.

An area integration method of pulse oximetry algorithm is described here suited to oxygen saturation estimation for both low perfusion and movement pulse wave. We remove the base line drift of pulse wave, and integrate the pulse wave of red and infrared separately to remove the noise. It is proven that the ratio of the area is equal to the ratio ac part of pulse wave. We can estimate the SpO2 accurately by this algorithm, and the result of the SpO2 estimation is compared with a golden standard blood gas analysis method.

Dynamic localization and quasi-Bloch oscillations in general periodic ac-dc electric fields

We examine the conditions for dynamic localization in general applied periodic ac-dc electric fields. We find that in the presence of both ac and dc components to the field, in addition to traditional dynamic localization, a different type of dynamic localization can occur irrespective of the shape and amplitude of the ac part of the field. These ``quasi-Bloch oscillations'' take place if the ratio of the Bloch frequency to the ac frequency is a noninteger rational number. Quasi-Bloch oscillations occur only within the tight-binding approximation, but are not restricted to the nearest-neighbor tight-binding limit. This type of dynamic localization provides a more experimentally accessible way to observe dynamic localization in an electronic system than conventional dynamic localization.

A New Approach For Modelling of Multiterminal DC System in Load Flow Programs

The conventional methods of the DC network modelling in the existing AC load flow program need structural changes in the AC part. As a result, in the case of an advanced AC program this combination becomes a difficult and complex programming effort.This paper presents a new and practical approach for solving the AC-DC load flow problem, whose DC system can be a multiterminal DC network. The presented approach just models the converters and it uses the AC load flow to solve other parts of DC network with a simple transformation.

Ac conductance of a magnetic multilayer structure with internal potential

The transport properties of a magnetic multilayer structure under a low-voltage and low-frequency perturbation are investigated. The theory is based on the ac linear response approximation developed by B\"uttiker et al. In the numerical calculations, the scattering matrix method is used. Also the calculations are self-consistent in order to take into account the internal potential caused by charge interactions inside the system. The numerical results reveal the transmission probabilities, dynamic admittance, and internal potential distributions under the changes of magnetic field and incident electron energy. The dc part and ac part of the conductance are dependent on the magnetic field strength, the size of the system, and the incident electron energy. In particular, the ac part of the conductance depends also on the wave-vector. This characteristic can be used to realize the wave-vector filtering device under ac perturbation. More interesting is that a transformation can be fulfilled between the inductive and capacitive behavior by tuning the magnetic field.

Estimation of the flux linkage in a direct-torque-controlled drive

An improved integration method is presented for the estimation of the stator flux linkage for speed- and position-sensorless direct-torque-controlled AC machine drives. The method is based on monitoring the scalar product of the estimated stator flux linkage and the measured stator current. The AC part of the scalar product is extracted using filtering and the correction for the estimated stator flux linkage is formed from that part. Adequate performance is obtained by using simple low-pass filtering. By using adaptive filtering in the extraction, the performance of the drive is excellent. Both simulation and laboratory test results are presented, which show that the presented method works well both in steady state and in transients.

Open-circuit test of a PZT vibrator and its applications

This study investigates a terminal transient response of a Langevin-type PZT vibrator theoretically and experimentally to quantify an electrical shock and refine an equivalent circuit of the vibrator. The shock is induced immediately after an AC sinusoidal voltage of the vibrator is switched off. Then, the transient response involves a DC part and an AC part, which approach zero at the DC and AC times, respectively, and the vibrator is placed on a sponge in air. To do so, we should propose an open-circuit test to find the AC and DC times in addition to the maximum amplitude of the transient response. Thus the DC times exceeds the AC time, and the AC and DC times are used to estimate the resistances in the equivalent circuit presenting the real mechanical and dielectric losses, respectively. Therefore, the resistances in the equivalent circuit are sensitive to the vibration amplitude, but the inductance and capacitances are not. Furthermore, the maximum amplitude is required to cause the shock, and depends on the frequency of the source and the open-circuited time, and is about 65 times the amplitude of the source.

A new method for magnetic position and orientation tracking

The method is based on two-axis generation of a quasi-static rotating magnetic field and three-axis sensing. Two mutually orthogonal coils fed with phase-quadrature currents comprise the excitation source, which is equal to a mechanically rotating magnetic dipole. The resulting excitation field rotates elliptically at any position in the near-field region. The AC part of the squared field magnitude is a sinusoidal wave at twice the excitation frequency. The following set of parameters uniquely characterize the excitation at the sensor's position: the phase of the squared field waveform, relative to the excitation currents, the minimum field value, the ratio of the field extremes, and the orientation of the excitation field plane. Simple and explicit analytical expressions are given which relate the first three parameters to the azimuth, elevation, and distance from the source to the sensor, respectively. The orientation of the sensor axes, relative to the plane of the excitation, can easily be determined by comparing the phase and amplitude of the measured signals against the phase and amplitude of the excitation field at the sensor's position. Apart from simplicity, the proposed method increases the speed of tracking; a single period of excitation is in principle sufficient to obtain all of the information needed to determine both the sensor's position and orientation. A continuous sinusoidal excitation mode allows an efficient phase-locking and accurate detection of the sensor output. It also improves the electromagnetic compatibility of the method.

Alternating current susceptibility measurements of inter-grain critical current density in sintered Bi1.8Pb0.2Sr2Ca2Cu3Oy

The critical index of inter-grain penetration field Hp* was estimated for sintered Bi1.8Pb0.2Sr2Ca2Cu3Oy high Tc superconductor by ac magnetic susceptibilities ac.0´, real part of the linear ac, showed two successive diamagnetic transitions at Tc = 107.8 K and Tc* = 104.6 K for intra- and inter-grain parts, respectively. Below Tc*, 0´´, the imaginary part of the linear ac, appeared and had a positive peak. The temperature and field dependences of 0´´ below Tc* were analysed by the Bean critical state model for the slab geometry on the basis of qualitative agreements of real and imaginary third harmonic components, 2´ and 2´´, respectively. The obtained Hp* well reproduced the results of 0´. The critical index of inter-grain critical current density Jc* was estimated as 2.8 from the relation of Jc* Hp*(1-T/Tc*). The large value of was significant for the present Bi2223 high Tc ceramics.

New space-vector control strategies for three-phase step-up/down AC/DC converter

In this paper, an equivalent DC duty cycle for the generalized zero-voltage space vectors is proposed such that control of the three-phase AC part and the DC part of the converter circuit can be integrated to achieve the ideal characteristic of single-stage step-up/down AC/DC converter. Depending upon how many modes are chosen and which class of generalized zero-voltage space vectors is selected to increase the equivalent DC duty cycle, different control strategies can be obtained. It is seen that not only the control of the six switches is simplified but also the deadtime circuit for avoiding short circuit of the same arm can be eliminated for the proposed converter. In addition, some guidelines for selecting the LC parameters are described briefly and experimental results given for verifying the validity of the proposed converter.

Two functionally dependent acetylcholine subunits are encoded in a single Caenorhabditis elegans operon.

The deg-3 gene from the nematode Caenorhabditis elegans encodes an alpha subunit of a nicotinic acetylcholine receptor that was first identified by a dominant allele, u662, which produced neuronal degeneration. Because deg-3 cDNAs contain the SL2 trans-spliced leader, we suggested that deg-3 was transcribed as part of a C. elegans operon. Here we show that des-2, a gene in which mutations suppress deg-3(u662), is the upstream gene in that operon. The des-2 gene also encodes an alpha subunit of a nicotinic acetylcholine receptor. As expected for genes whose mRNAs are formed from a single transcript, both genes have similar expression patterns. This coexpression is functionally important because (i) des-2 is needed for the deg-3(u662) degenerations in vivo; (ii) an acetylcholine-gated channel is formed in Xenopus oocytes when both subunits are expressed but not when either is expressed alone; and (iii) channel activity, albeit apparently altered from that of the wild-type channel, results from the expression of a u662-type mutant subunit but, again, only when the wild-type DES-2 subunit is present. Thus, the operon structure appears to regulate the coordinate expression of two channel subunits.

Silicon Rapid Thermal Processing with Ripple Pyrometry

ABSTRACTThermal processing in silicon integrated circuit fabrication steps for dopant activation, metal silicides, annealing, and oxidation commonly uses single-wafer furnaces that rapidly heat wafers with incandescent infrared lamps. Radiation pyrometers and thermocouple probes are the principle methods of measuring wafer temperature for closed-loop control of rapid thermal processes. The challenge with thermocouples is in dealing with heat from the lamps and non-ideal thermally resistive wafer contact. The challenge with pyrometry is in compensating for the variable emissivity of wafer surfaces and suppressing interference from the lamps. Typical deposited or grown layers of silicon nitride, silicon dioxide, and polycrystalline silicon can produce dramatic changes in emissivity. Layer thicknesses and composition are generally not known with sufficient accuracy, so a method for real time in situ emissivity compensation is required. Accufiber introduced a “ripple technique” to address this issue. The idea is to use two probes, separately sensing radiation from the wafer and the lamps, and extracting AC and quasi-DC parts from each. The AC signals provide a measure of the reflectivity of the wafer, and thence emissivity, as well as the fraction of reflected lamp radiation present in the DC signals. Lucent Technologies introduced a method of using AC lamp ripple to measure wafer temperatures with two radiation probes at a wall in the furnace. One probe views radiation emanating from the wafer through a gap in the lamp array. The other probe has a wide field of view to include lamp radiation. The accuracy of Lucent devices, determined from process results on wafers with various emissivities, is typically in the range of 12°C to 18°C at three standard deviations.

Reconstruction of the mass distribution of charged particles in a periodic electric field

A method is proposed for determining the mass spectrum of a monochromatic precisely directed source by means of a plane-parallel capacitor with a sinusoidally time-dependent voltage on the plates. The mass spectrum is reconstructed from an integral equation that relates the current to the collector with the amplitude of the ac part of the voltage.

A self-stabilizing Ac derivative and its potential for transposon tagging.

With the goal of developing a self-stabilizing transposon tagging system, a derivative of the maize transposable element Ac (Ds303) harbouring a deletion between bp 246 and 736 has been introduced into tomato (Lycopersicon esculentum) by Agrobacterium tumefaciens-mediated transformation. The deletion removes the major transcription start site, 84 bp of the putative Ac promoter and part of the untranslated leader. Transpositions from the T-DNA, where Ds303 was inserted between the mannopine synthase 1' promoter and the GUS gene, were observed in four independent transgenic plants analysed. After transposition the transposed Ds303 elements were stably integrated in the genome and could not transactivate a tester Ds element. However, somatic and germinal transpositions of the transposed Ds303 elements occurred in the presence of a transposase source.

Exhaustible Resources, Non-Convex Costs and Contestability. A Reply

In his comment on my paper, Geir Asheim neatly disproves the arguments in my (1991) footnote 13 and the paragraph to which it refers. Trying to force the equilibrium into the mould of contestability, I was unmindful of the possibility that there could be a period when all firms produced. This possibility allows for Asheim's interesting observations, including that Ramsey prices result when price taking can be assumed if all firms are active. To begin I wish to stress the points which have been established in the two papers. First, equilibrium must satisfy two types of intertemporal arbitrage condition, a marginal and an average one. The novel condition is the latter, the contribution of contestability theory. Satisfying it leaves no incentive to reallocate a discrete amount of production to another time period. It helps give rise to what seems to be an unusual, hybrid sort of rent that Asheim identifies as the user cost: when contestability holds sway, it is price less average, not marginal, cost which rises at the rate of interest. Links to the more customary form of user cost, however, can be discerned in the marginal condition, which is necessary to preclude incentives to reallocate production at the margin among time periods. Newbery (1981) calls this Hotelling's arbitrage principle. It appears in Asheim's equation (2), since MR = P under his assumptions of first competition and then contestability.' On the downward-sloping part of AC, however, his equation

Ac conductivity in ionically conducting crystals and glasses

The ac conductivity behavior has been studied for crystalline oxygen-ion conductors: CeO 2:Gd 3+ and CaTiO 3:Al 3+ as well several silicate and borate glasses over a wide range of temperature. In all cases, Jonscher's universal power law behavior: σ( ω)= σ(0)+ Aω s is observed, where σ(0) is the dc conductivity and s the power law exponent. Furthermore, there are three regions of behavior. At the higher temperatures, s is a constant (usually≈0.6) independent of T. In this range σ can be written in the form suggested by Almond and West: σ( ω)= σ(0)[1+( ωτ) s ]. We find that τ has the same activation energy as σ(0) and a pre-exponential ≈10 −14 s. However, the quality of the activation energies does not imply that all carriers are unassociated, as Almond and West have claimed. Rather, it suggests that the ac and dc parts of the conductivity are manifestations of a single hopping process involving ion-ion interactions. At lower temperatures, the exponent s increases as T decreases, finally leveling off at s=1.

Determination of commutating voltage and commutation reactance and computation of three-phase AC/DC power flow

This paper presents a rigorous method of determining the commutating voltage and the commutation reactance, both of which play significant roles in the analysis of AC/DC power systems under unbalanced AC conditions. An accurate but simple three-phase no-mutual equivalent circuit is derived for the AC part connected to the three-phase converter bridge. By using the circuit, the analyses relevant to AC/DC power systems under both steady state and dynamic unbalanced conditions could be performed more precisely and more concisely. As an application, three-phase AC/DC power flow is also discussed. A set of complete but minimized converter equations is developed, with which the computational requirements of the power flow could be reduced.

The use of transgenic plants to understand transposition mechanisms and to develop transposon tagging strategies.

This review compares the activity of the plant transposable elements Ac, Tam3, En/Spm and Mu in heterologous plant species and in their original host. Mutational analysis of the autonomous transposable elements and two-element systems have supplied data that revealed some fundamental properties of the transposition mechanism. Functional parts of Ac and En/Spm were detected by in vitro binding studies of purified transposase protein and have been tested for their importance in the function of these transposable elements in heterologous plant species. Experiments that have been carried out to regulate the activity of the Ac transposable element are in progress and preliminary results have been compiled. Perspectives for manipulated transposable elements in transposon tagging strategies within heterologous plant species are discussed.