Optimum Current Level Research Articles

Investigation of photovoltaic thermoelectric air-conditioning system for room application under tropical climate

Photovoltaic thermoelectric air-conditioning system (PT A/C) system could be a greater option compared to conventional A/C system as it is Freon-free and absence of moving parts. This study investigated the cooling and dehumidification performance of a PT A/C that is solely powered by solar energy under tropical climate conditions. The system is built with 9 pieces of thermoelectric to provide cooling for a test chamber of 3.6 m3 volume. The effect of input current on the system’s cooling and moisture removal rate were investigated and results showed that 5 A is the optimum current level, providing an average of 181 W cooling capacity and 0.14 ltr/hour of moisture removal rate at the given ambient conditions. During the operation, indoor temperature of the test chamber was 4 °C lower than the unconditioned chamber and 7.7 °C compared to the ambient temperature. Whereas the indoor relative humidity varies between 58~83 %. Furthermore, for a 12 hours operation, the system consumes 1.45 kWh of energy, and delivered temperature between 23.8 to 27.8 oC at 5 A.

Low-frequency noise of GaN-based ultraviolet light-emitting diodes

Low-frequency fluctuations of current and light intensity were measured for different types of ultraviolet (UV) light-emitting diodes (LEDs) with wavelengths from 280 to 375 nm. These UV LEDs are suitable for studying steady-state and time-varying UV fluorescences of biological materials. The correlation coefficient between the current and light intensity fluctuations varies with the LED current and load resistance. This dependence is explained in terms of contributions to the 1∕f noise from the active region and from the LED series resistance. The noise level could be reduced by operating the UV LEDs at a certain optimum current level and with large external series resistance.

Control of the crystallite size and passivation of defects in porous silicon by a novel method

Porous silicon films were prepared by lateral anodization of crystalline silicon in HF based solutions at different current densities. At an optimum current density, passivation of the defects by an appropriate post-anodization treatment results in the significant enhancement in the photoluminescence (PL) efficiency. However, above the optimum current level, a phase is obtained which shows significant broadening of the PL spectrum indicating the quantum wire size distribution. The degraded PL intensity in the treated samples is higher as compared to that for the as-anodized samples. Infrared vibrational studies indicate that this enhancement is due to the H-passivation of defects in the Si-pore interface, though the presence of hydrogen-terminated silicon clusters cannot be ignored. Capacitance–voltage studies concur well with the photoluminescence and infrared results.

Electrical Techniques for Stimulation of the Phrenic Nerve to Pace the Diaphragm: Inductive Coupling and Battery Powered Total Implant in Asynchronous and Demand Modes

A review of the electrical design of a rf inductively coupled phrenic nerve stimulator for the diaphragm developed in our laboratories will be discussed. Modifications of the original circuit are based on long-term laboratory and clinical studies. A total implant battery powered stimulator was designed exclusively for animal studies to evaluate the effects of several stimulating parameters on diaphragm fatigue and neuromuscular structure. On the basis of these studies the optimum current level, stimulus frequency, respiratory rate, electrode configuration, and waveform were selected for clinical use to pace the diaphragm. A multiprogrammable dual output stimulator responsive to interrogation has been constructed and used in the experimental laboratory in anticipation of clinical application. There was an insignificant difference between the effect on neural structure or diaphragm function of stimulation with pulse width modulated constant voltage or with amplitude-modulated constant current. Demand pacing: maintenance of normal PACO2 by monitoring ET PACO2 with feedback to the diaphragm pacemaker to adjust the pacing rate has been successful in the experimental animal.

Stimulation-produced analgesia: Evidence for somatotopic organization in the midbrain

The somatotopic organization of structures in the midbrain which mediate stimulation-produced analgesia (SPA) was studied by stimulating a series of neural loci using a movable electrode. The strength and distribution of analgesia at 7 fields on the body surface, as measured by the application of noxious pinch, was clearly related to the dorsoventral stimulation locus. SPA at dorsal sites was distributed at the ears and, to a lesser extent, at the forepaws. At progressively more ventral loci, maximal analgesia appeared successively at the forepaws, hindpaws and tail. This organization was organization was maintained throughout the rostrocaudal extent of the midbrain. However, rostral stimulation sites tended to produce analgesia in smaller, more discrete fields than those produced by caudal stimulation sites. Further studies showed that the relationship between SPA and stimulation site is influenced by the electrical stimulation current level. Each site had an optimum current level, so that current intensities higher or lower than the optimum produced decreased analgesia. These results reveal a possible neural mechanism for somatotopic organization in hyperstimulation analgesia in which an intense somatic input at a body site produces analgesia in the same or adjacent segments.

Theoretical and Experimental Evaluation of RZ and NRZ Recording Characteristics

RZ and NRZ recorded pulse characteristics are determined theoretically and verified experimentally. Quantitative expressions are derived for the pulse location, width, shape and amplitude as a function of input current, head-tape spacing and gap width. The analysis is based upon the arctangent approximation for the head longitudinal field component and an empirical (also arctangent) expression for the tape magnetization curve. From the analysis, not only the effect, but the separate effects of field shape and magnetization curve on the pulse characteristics can be evaluated. It is shown that as the current increases, the pulse moves from the gap edge region towards the gap center line and then out again. The amount of pulse displacement, as a function of current, increases rapidly with larger head-to-tape spacing. The record drop-out sensitivity is directly related to the location of the pulse for NRZ peak sensing systems. At an optimum current level for different spacings, the location of the recorded pulse is found to be almost fixed; that is to say, the recorded dropout does not appear as a shift in pulse location but only as a drop in pulse amplitude. Since for small current and thus for small fields the remanent magnetization on the tape is approximately proportional to the applied field, the shape of the recorded magnetization, hence the recorded pulse, is given by the shape of the record head field.