Biosynthesis, structure, and biological activities of envelope protein gp65 of murine coronavirus.

We have previously shown that gp65 (E3) is a virion structural protein which varies widely in quantity among different strains of mouse hepatitis virus (MHV). In this study, the biosynthetic pathway and possible biological activities of this protein were examined. The glycosylation of gp65 in virus-infected cells was inhibited by tunicamycin but not by monensin, suggesting that it contains an N-glycosidic linkage. Glycosylation is cotranslational and appears to be complete before the glycoprotein reaches the Golgi complex. Pulse-chase experiments showed that this protein decreased in size after 30 min of chase, suggesting that the carbohydrate chains of gp65 undergo trimming during its transport across the Golgi. This interpretation is supported by the endoglycosidase treatment of gp65, which showed that the peptide backbone of gp65 did not decrease in size after pulse-chase periods. This maturation pathway is distinct from that of the E1 or E2 glycoproteins. Partial endoglycosidase treatment indicated that gp65 contains 9 to 10 carbohydrate side chains; thus, almost all of the potential glycosylation sites of gp65 were glycosylated. In vitro translation studies coupled with protease digestion suggest that gp65 is an integral membrane protein. The presence of gp65 in the virion is correlated with the presence of an acetylesterase activity. No hemagglutinin activity was detected

Formation and Dissociation of Phosphorylated Peptide Radical Cations

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On the color stability of phosphor-converted white LEDs under DC, PWM, and bilevel drive

Most commercial white LEDs are made from nitride-based blue LEDs coated with yttrium aluminium garnet phosphor, which produce spectra that shift in opposite directions under the influences of drive current and junction temperature changes. This property gives rise to different emitted spectra, hence chromaticity properties, when the LED is driven/dimmed by different current waveforms. By using a commercial white LED sample, LUXEON K2, the effects of drive current and junction temperature on the changes of chromaticity coordinates are studied experimentally. The impact of dc, pulse width modulation (PWM), and bilevel current waveform is discussed through a graphical analysis, followed by experimental verification. It is proven that dc offers the best color stability over dimming due to the counteracting influences of drive current and junction temperature variations, whereas an LED constantly suffers from noneliminable chromaticity changes when driven by the PWM. Theoretical explanations are given to justify these cases, and it is found that, for the case of dc drive, an ideal heat sinks thermal resistance can be selected based on a simple equation to minimize the overall chromaticity change over dimming. This paper provides an in-depth discussion on the relations between the chromaticity properties of phosphor-converted (pc) white LEDs and the driving/dimming methods used. © 2011 IEEE.published_or_final_versio

Analysis on accuracy of charge-pumping measurement with gate sawtooth pulses

Charge-pumping (CP) measurement is performed on MOSFETs with their gates tied to sawtooth pulses. Influence of both rise time (tr) and fall time (tf) on the CP current of the devices with different channel lengths is investigated at different pulse frequencies. Results show that the dominant mechanism affecting the measurement accuracy is the energy range of interface-trap distribution Dit(E) swept by the gate signal for frequencies below 500 kHz and carrier emission for frequencies above 500 kHz. For frequencies higher than 600 kHz, incomplete recombination could be an additional mechanism when tf is too short. Hence, it is suggested that low frequency is more favorable than high frequency, especially for sawtooth pulses with long tr and short tf , due to little carrier emission and negligible geometric effects even for devices as long as 50 μm. However, if high frequency (e.g. 1 MHz) is required to obtain a sufficiently large S/N ratio in the CP current, sawtooth pulses with equal tr and tf should be chosen for the least carrier emission effect and thus more reliable results on interface-state density, Moreover, for both sawtooth and trapezoidal pulses with a typical amplitude of 5 V, a lower limit of 200 ns for tr and tf is necessary to suppress all the undesirable effects in devices shorter than at least 20 μm.published_or_final_versio

Stationary and adaptive color-shift reduction methods based on the bilevel driving technique for phosphor-converted white LEDs

The bilevel driving technique has realized a 2-D control of the luminosity and emitted color of white LEDs with duty cycle and forward current levels. Unfortunately, various combinations of these dimming control parameters can lead to significant changes in junction temperature, which further modify the luminosity and emitted color of LEDs. In this paper, the theoretical aspects of these complex interactions and the impact of bilevel drive on the color-shift properties of white LEDs are discussed in detail by using a mathematical color-shift model. Two color-shift reduction methods are proposed based on the insights obtained from this model. This study shows that a heat sinks thermal resistance that minimizes the overall color shift over dimming can be uniquely determined from the knowledge of some measurable LED parameters, and gives rise to a global minimum color shift. If such a thermal resistance cannot be realized due to practical limitations, the second method that utilizes an adaptive change of forward current levels over dimming can be adopted. Based on their nature, these methods are classified as stationary and adaptive methods, respectively. Their validity is supported by experimental measurements on a commercial white LED. © 2011 IEEE.published_or_final_versio

A pulsewidth modulation based integral sliding mode current controller for boost converters

Author name used in this publication: Chi K. TseRefereed conference paper2005-2006 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

Synthesis of input-rectifierless AC/DC converters

This paper discusses the basic construction procedure and topological possibilities of creating ac/dc converters out of simple dc/dc converters. It is shown that two separately controlled dc/dc converters are sufficient for producing a regulated dc output and shaping the input current, from an ac voltage source, without the need for input rectifiers. Some design constraints are discussed, emanating from the limitation of the conversion ratios that can be achieved by particular dc/dc converters. Selected topologies are verified experimentally. This kind of rectifierless converters find applications in airborne power supplies where zero-crossing distortions are significant because of the inevitable phase-lead effect of the input rectifier bridge.published_or_final_versio

Synthesis of input-rectifierless AC-DC converters

This paper discusses the basic construction procedure and topological possibilities of creating ac/dc converters out of simple dc/dc conveners. It is shown that two separately controlled dc/dc conveners are sufficient for producing a regulated dc output and shaping the input current, from an ac voltage source, without the need for input rectifiers. Some design constraints are discussed, emanating from the limitation of the conversion ratios that can be achieved by particular dc/dc converters. Selected topologies are verified experimentally.published_or_final_versio

A PFC topology with low input current distortion suitable for aircraft power supplies

This paper presents an AC-DC converter topology for realization of PFC converters for applications where the mains frequency is high and a low input current harmonics is required, e.g., in aircraft power systems. The proposed topology eliminates crossover distortion due to the presence of input rectifiers and the inevitable input current phase lead. The idea is to stack a DC voltage on top of the AC mains voltage to prevent voltage polarity reversal in the input, eliminating the input bridge rectifier. This eliminates the crossover distortion, which can be significant for supply systems having a high mains frequency. In addition, the proposed PFC converter allows bi-directional energy flow, ensuring all inductors work in continuous conduction mode and hence eliminating the distortion due to the abrupt change of dynamic response when the operating mode changes. Analysis and design of the power and control circuits will be given and discussed. An experimental system will be presented for verification purposes.published_or_final_versio