Complete Turn-off Research Articles

Multistate Circularly Polarized Luminescence Switching through Stimuli-Induced Co-Conformation Regulations of Pyrene-Functionalized Topologically Chiral [2]Catenane.

Aiming at the construction of novel circularly polarized luminescence (CPL) switches with multiple switchable emission states and high dissymmetry factors (glum ), topologically chiral [2]catenanes were employed as the key platform to construct a novel multistate CPL switching system. Taking advantage of the precise co-conformation regulations of the resultant pyrene-functionalized [2]catenanes under different external stimuli, reversible transformations between three emission states with different CPL performances, i.e. the initial "closed" form with a |glum | value of 0.012, the "open" form with an almost complete turn-off of CPL emission, and the "protonated" form with a boosted |glum | value of 0.022, were successfully realized. This study demonstrates the successful construction of not only the first topological chirality-based CPL switch, but also a novel bidirectional CPL switch, thus providing a promising platform for the construction of novel chiral materials.

V4743 Sgr, a magnetic nova?

Two XMM Newton observations of Nova V4743 Sgr (Nova Sgr 2002) were performed shortly after it returned to quiescence, 2 and 3.5 years after the explosion. The X-ray light curves revealed a modulation with a frequency of ~0.75 mHz, indicating that V4743 Sgr is most probably an intermediate polar (IP). The X-ray spectra have characteristics in common with known IPs, with a hard thermal plasma component that can be fitted only assuming a partially covering absorber. In 2004 the X-ray spectrum had also a supersoft blackbody-like component, whose temperature was close to that of the white dwarf (WD) in the supersoft X-ray phase following the outburst, but with flux by at least two orders of magnitude lower. In quiescent IPs, a soft X-ray flux component originates at times in the polar regions irradiated by an accretion column, but the supersoft component of V4743 Sgr disappeared in 2006, indicating a possible origin different from accretion. We suggest that it may have been due to an atmospheric temperature gradient on the WD surface, or to continuing localized thermonuclear burning at the bottom of the envelope, before complete turn-off. An optical spectrum obtained with SALT 11.5 years after the outburst showed a prominent He II 4686A line and the Bowen blend, which reveal a very hot region, but with peak temperature shifted to the ultraviolet (UV) range. V4743 Sgr is the third post-outburst nova and IP candidate showing a low-luminosity supersoft component in the X-ray flux a few years after the outburst.

Axial p–n Nanowire Gated Diodes as a Direct Probe of Surface-Dominated Charge Dynamics in Semiconductor Nanomaterials

Axially doped p–n silicon nanowire (SiNW) gated diodes are fabricated, and their electrical properties are investigated to demonstrate the enhanced surface effects on the nanoscale devices of semiconductor nanomaterials. The fabricated p–n SiNW exhibited clear rectifying characteristics with an ideality factor of ∼2. More interestingly, the gated p–n SiNW showed a switching behavior as a function of the gate bias with almost complete turn-off of the forward current. The observed ideality factor and gated diode characteristics were explained with surface trap states of the nanowires. Systematic 3D device simulation quantitatively confirms that the surface states are a key factor in determining such surface-dominated characteristics. This work would serve the fundamental and in-depth understanding of the surface properties in the various nanoscale 1D devices.

Switching loss reduction through digital burst technique in TV power supply [From Mind to Market

Digital burst mode is an operation that can be used to control power transistor switching by the microprocessor signal. This also allows burst mode to be extended to future applications, such as multiple regulation in TV and other audio/video products. This technique substantially reduces stress for the main switching transistor during standby mode since it is not a complete turn-off.

Electronic transport in locally gated graphene nanoconstrictions

We have developed the combination of an etching and deposition techniques that enables the fabrication of locally gated graphene nanostructures of arbitrary design. Employing this method, we have fabricated graphene nanoconstrictions with local tunable transmission and characterized their electronic properties. An order of magnitude enhanced gate efficiency is achieved adopting the local gate geometry with thin dielectric gate oxide. A complete turn off of the device is demonstrated as a function of the local gate voltage. Such strong suppression of device conductance was found to be due to both quantum confinement and Coulomb blockade effects in the constricted graphene nanostructures.

Elucidation of the intrinsic loss arising from switch output capacitance Coss in ultra-high-speed low-loss power converters

Attempts to drive down the switching losses of hard-switched unipolar devices by increasing gate drive current levels are ultimately limited by the device output capacitance, which thus represents an intrinsic loss. The paper presents an in-depth analysis of the charging and discharging of the output capacitance and the associated loss producing mechanisms. It is shown that energy is stored in the depletion layer of the device during turn-off and then dissipated as heat during the turn-on process. The instantaneous power dissipated in the device is thus different to the instantaneous power loss measured at the device terminals, although the total energy loss over one complete turn-off and turn-on cycle is still faithfully reproduced. An analytical approach to determining the intrinsic switching loss due to the output capacitance is presented and verified by experimental results and by TCAD simulation. It is shown that around 20% of the total switching losses arise from the intrinsic output capacitance loss under fast-switched inductive load conditions. A comparison of Si and SiC FET devices demonstrates the potential for SiC power devices to provide an energy efficient option for very high frequency switching.

Software's secret sauce: the "-ilities" [software quality

If beauty is in the eye of the beholder, then quality must be as well. We live in a world where beauty to one is a complete turnoff to another. Software quality is no different. We have the developer's perspective, the end users perspective, the testers perspective, and so forth. As you can see, meeting the requirements might be different from being fit for a purpose, which can also be different from complying with rules and regulations on how to develop and deploy the software. Yet we can think of all three perspectives as ways to determine how to judge and assess software quality. These three perspectives tie directly to the persistent software attributes focus section in this issue and, consequently, to the concept of software "-ilities". The -ilities (or software attributes) are a collection of closely related behaviors that by themselves have little or no value to the end users but that can greatly increase a software application or system's value when added.

Turn-off operation of a 2.6 kV 4H-SiC gate turn-off thyristor in MOS-gate mode

The turn-off operation of a 4H-SiC gate turn-off thyristor with 2.6 kV breakover voltage has been studied in the MOS-gate mode by means of computer simulation. The turn-off was analyzed at different blocking voltages in the temperature range from 300 to 500 K. A good agreement between the simulation results and experimental data was demonstrated. It is shown that, according to the experiment, for complete turn-off of a thyristor in the MOS-gate mode, the duration of the turn-off pulse applied to the MOSFET gate, Δ t off, should be long enough (Δ t off>Δ t * off), where Δ t * off is the minimum duration of the turn-off pulse. The Δ t * off value depends rather weakly on the cathode blocking voltage V 0, despite the strong dependence of the critical charge density on V 0. It is shown that the long delay in the spontaneous switch-on, occurring at Δ t off⩽Δ t * off, is due to the very slow current rise at low injection level in the blocking p 0-base. An analytical theory of the current rise processes has been developed for the case when the current injection coefficients of the emitter–base junctions are not unity.

Effect of base parameters on the gate-controlled squeeze of a current-conducting region in pnpn structures

If a gate current is smaller than some critical value required for the complete turn-off of an anode current in a p +npn + -structure it produces the stationary squeeze of current-conducting region (CCR) and increase of the current density in it. The process of squeezing depends on a longitudinal conductivity of the controlling p-base which is electrically-connected with the gates. But the conductivity along the controlled n-base which is not connected with the gates affects the process of squeezing indirectly as well. This effect takes place mainly due to the current bias of a parasitic transistor which is formed in a depletion region of the structure and divides the substantial part of the gate current. Calculations of the CCR squeeze which take into account base conductivities are described in this work.

Relaxation of the dynamic magnetism of 3He-B. A simple study of the ?wall-pinned mode?

The equations of motion, including dissipation, for the dynamic magnetism of 3He-B following the complete turnoff of a small field are solved with the aim of demonstrating that two characteristic relaxation times may be distinguished. These are the rapid relaxation toward a rather long-lived mode (that turns out to involve an extremely simple motion), and the relaxation of this mode. The linear relaxation of the inverse frequency squared observed for the “wall-pinned mode” is rigorously justified, and corrections to the ideal case are discussed.

Cro regulatory protein specified by bacteriophage lambda. Structure, DNA-binding, and repression of RNA synthesis.

The Cro protein specified by bacteriophage lambda is a repressor of the genes expressed early in phage development and is required for a normal late stage of lytic growth. We have purified Cro protein to virtual homogeneity and analyzed its structure and properties as a DNA-binding protein and repressor of RNA synthesis. To confirm that the protein is the product of the cro gene, we have also shown that a missense mutation in the cro gene leads to a product that is more temperature- and salt-sensitive in its DNA-binding property. As purified, Cro protein is a dimer of identical subunits of molecular weight 8600. The purified protein binds to lambda-DNA carrying the specific binding sites (operators oL and oR) with an estimated dissociation constant of 10(-10) M to 10(-11) M; there is also weaker binding to other sites on DNA, as found for other DNA-binding regulatory proteins. In a purified transcription system, the Cro protein is an effective and specific repressor of RNA synthesis from the N and cro genes; thus Cro is an autorepressor which regulates its own synthesis. A comparison of the properties of the two lambda repressor proteins, cI and Cro, indicates that cI is a "strong repressor" specialized for complete turnoff of lytic functions needed for the maintenance of lysogeny, whereas Cro is a "weak repressor" specialized for a gradual turnoff of early viral genes that potentiates the late stage of lytic development.

Control of synthesis of mRNA's for T4 bacteriophage-specific dihydrofolate reductase and deoxycytidylate hydroxymethylase.

A 30 degrees C, functional messengers for dCMP hydroxymethylase first appeared 3 to 6 min postinfection and reached their maximum levels at 12 min. Chloramphenicol, added before the phage, reduced the rate of mRNA accumulation. When the antibiotic was added 6 min postinfection, mRNA levels increased at their normal rate but there was no obvious repression of messenger accumulation. Delaying the addition of drug until 8 or 12 min had progressively less effect on the pattern of hydroxymethylase mRNA metabolism. When chloramphenicol was present from preinfection times or from 6 min postinfection, all hydroxymethylase mRNA's synthesized were stable; at later times, however, the ability of the drug to stabilize mRNA decreased with its ability to delay the turnoff of mRNA production. An overaccumulation of hydroxymethylase mRNA was also seen when phage-specific DNA synthesis was inhibited either by mutational lesion in an essential viral gene or by 5-fluorodeoxyuridine. By min 20 of a DNA-negative program, hydroxymethylase mRNA synthesis was repressed to the point where it no longer compensated for decay. However, a finite level of hydroxymethylase mRNA synthesis was maintained at later times of a DNA-negative infection. Such results indicate that replication of the phage chromosome is necessary but not sufficient for a complete turnoff of hydroxymethylase mRNA production. Functions controlled by the maturation-defective proteins (the products of genes 55 and 33) played only a minor role in the regulation of hydroxymethylase mRNA, metabolism. Thus, we favor the hypothesis that a complete turnoff of hydroxymethylase messenger production requires one or more new proteins as well as an interval of DNA replication. The absence of DNA synthesis had no particular effect upon dihydrofolate reductase messenger production. The preinfection addition of chloramphenicol likewise had little effect on dihydrofolate reductase messenger metabolism. These latter data imply that prior synthesis of a phage-coded protein synthesis may not be required for the turnoff of reductase messenger production.

Turn-off transient behaviour of p- i- n diodes

The transient turn off behaviour of a p- i- n diode (or a p +- n- n + diode under high level injection conditions) is studied. The paper examines in detail the various phases occuring under conventional ‘current switching’ conditions after the end of the constant reverse current phase. The paper is divided into two parts which deal respectively with the slow transient (evacuation of the residual charge in the neutral region) and the following fast transition (evacuation of the ‘left over charge’ in the space charge region and charging of the space charge capacitance). The results presented enable the complete turn off behaviour for various diodes to be predicted with a fair degree of accuracy, as is shown by the experimental results. For the slow transient, both constant carrier velocity and constant mobility conditions are considered with variable current, i.e. the interaction between the external circuit (characterized by a constant reverse voltage and a series resistance) and the diode parameters is taken into account. The voltage at the end of this slow transient is determined and related to diode and circuit parameters. The voltage at which the change over from constant mobility to constant velocity conditions occurs is also determined. For the fast transition, the interaction between the circuit and device parameters is again considered and evaluation of the two times characterizing this fast transition enables the voltage versus time decay to be characterized for any diode and circuit parameters. The conditions necessary for the fast transition to exist are discussed and the optimum condition for the fastest ‘turn off’ is determined, which in turn determines the ultimate limit of a step recovery diode.