3,196 research outputs found
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BOAT: Building auto-tuners with structured Bayesian optimization
Due to their complexity, modern systems expose many con-figuration parameters which users must tune to maximizeperformance. Auto-tuning has emerged as an alternative inwhich a black-box optimizer iteratively evaluates configura-tions to find efficient ones. Unfortunately, for many systems,such as distributed systems, evaluating performance takestoo long and the space of configurations is too large for theoptimizer to converge within a reasonable tim
The Effect of ArF-Excimer Laser Irradiation of the Human Enamel Surface on the Bond Strength of Orthodontic Appliances
This study investigated enamel laser conditioning as an alternative to acid etching in bracket therapy. In preliminary experiments optimal laser parameters for achieving a bond strength of 6-10 N/mm2 were defined. Enamel surface morphology was assessed and the ablation depth was measured on serial enamel sections. Thirty human molars were exposed to 193 nm ArF-excimer laser radiation (energy density: 260 mJ/cm2) by single pulse application of 23 nanoseconds. Thirty molars were etched with phosphoric acid (37%) for 60 seconds. The brackets from the treated molars and 30 untreated molars were debonded vertically for tensile bond strength measurement. Roughened enamel surfaces were attained by 450 and 900 laser pulses with a mean ablation depth of 10.13 ± 4. 84 Όm. After 1-10 laser pulses, the enamel surface appeared intact. The tensile bond strength was 6.63 ± 2 .18 N/mm2 in the laser-treated group (1 pulse), 8.75 ± 3.61 N/mm2 in the acid-etched group, and 4 .61 ± 3.15 N/mm2 in the untreated group. We conclude a laser-selective ablation of the membranous enamel pellicle. Since the irradiated area can be adapted to bracket base and the enamel surface remains morphologically intact, pulsed ArF-excimer laser treatment seems to be superior to the acid etching technique
The Resistive-Plate WELL with Argon mixtures - a robust gaseous radiation detector
A thin single-element THGEM-based, Resistive-Plate WELL (RPWELL) detector was
operated with 150 GeV/c muon and pion beams in Ne/(5%CH), Ar/(5%CH) and
Ar/(7%CO); signals were recorded with 1 cm square pads and SRS/APV25
electronics. Detection efficiency values greater than 98% were reached in all
the gas mixtures, at average pad multiplicity of 1.2. The use of the
10{\Omega}cm resistive plate resulted in a completely discharge-free
operation also in intense pion beams. The efficiency remained essentially
constant at 98-99% up to fluxes of 10Hz/cm, dropping by a few %
when approaching 10 Hz/cm. These results pave the way towards
cost-effective, robust, efficient, large-scale detectors for a variety of
applications in future particle, astro-particle and applied fields. A potential
target application is digital hadron calorimetry.Comment: presented at the 2016 VIenna Conf. On instrumentation. Submitted to
the Conference proceeding
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Quaestor: Query web caching for database-as-a-service providers
Today, web performance is primarily governed by round-trip latencies between end devices and cloud services. To improve performance, services need to minimize the delay of accessing data. In this paper, we propose a novel approach to low latency that relies on existing content delivery and web caching infrastructure. The main idea is to enable application-independent caching of query results and records with tunable consistency guarantees, in particular bounded staleness. Q
uaestor
(Query Store) employs two key concepts to incorporate both expiration-based and invalidation-based web caches: (1) an Expiring Bloom Filter data structure to indicate potentially stale data, and (2) statistically derived cache expiration times to maximize cache hit rates. Through a distributed query invalidation pipeline, changes to cached query results are detected in real-time. The proposed caching algorithms offer a new means for data-centric cloud services to trade latency against staleness bounds, e.g. in a database-as-a-service. Q
uaestor
is the core technology of the backend-as-a-service platform Baqend, a cloud service for low-latency websites. We provide empirical evidence for Q
uaestor
's scalability and performance through both simulation and experiments. The results indicate that for read-heavy workloads, up to tenfold speed-ups can be achieved through Q
uaestor
's caching.
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Numerical and Experimental Demonstration of Intermodal Dispersive Wave Generation
Abstract Evidence of intermodal dispersive wave generation mediated by intermodal crossâphase modulation (iXPM) between different transverse modes during supercontinuum generation in silicon nitride waveguides is presented. The formation of a higherâorder soliton in one strong transverse mode leads to phase modulation of a second, weak transverse mode by iXPM. The phase modulation enables not only supercontinuum generation but also dispersive wave generation within the weak mode, that otherwise has insufficient power to facilitate dispersive wave formation. The nonlinear frequency conversion scheme presented here suggests phaseâmatching conditions beyond what is currently known, which can be exploited for extending the spectral bandwidth within supercontinuum generation.Intermodal dispersive wave generation mediated by intermodal crossâphase modulation between different transverse modes during supercontinuum generation in silicon nitride waveguides is demonstrated. The phase modulation enables dispersive wave generation within a weak mode, that otherwise has insufficient power to facilitate dispersive wave formation. This process suggests new phaseâmatching conditions for frequency conversion beyond to what is currently known. imag
Effects of Aperture Size on <i>Q</i>Â factor and Shielding Effectiveness of a Cubic Resonator
The EMC properties of a cubic metallic shield are highly affected
by its resonances. At the resonant frequencies, the shielding effectiveness
(SE) collapses, which results in high field strengths inside the cavity. This
can cause failure or even breakdown of electronic devices inside the shield.
The resonant behaviour is mainly determined by the quality or QÂ factor of
the shield. In this paper, the effects of the aperture size on the QÂ factor
and the SE of an electrically large, cubic shield are analysed. At first, a
method is developed in order to determine the QÂ factor based on the
resonance behaviour of the shield in time domain. Only the first resonance of
the shield is considered therefore. The results are evaluated for different
aperture diameters and compared with theory for the QÂ factor. The dominant
coupling mechanism of electromagnetic energy into the shield is thus
identified.
Then the effect of aperture size on the SE is analysed. The excitation of
resonances is very probable if the interfering signal is an ultrawideband
(UWB) pulse, which constitutes a typical intentional electromagnetic
interference (IEMI) scenario. Therefore, the relation between aperture size
and SE is analysed using the theory of the transient SE for a broadband
signal with a constant spectral density distribution. The results show, that
a worst case aperture size exists, where the SE has its minimum
Calculation of the Combined Electric Field Response of Multiple Nonlinear Antenna Loads due to HPEM Excitation
The electromagnetic properties of receiving and scattering structures with nonlinear components are difficult to predict, especially if more than one nonlinear load is involved. In this contribution a frame antenna with two diodes that act as nonlinear loads is analyzed. This receiving antenna structure is illuminated by a polarized plane wave, carrying a transient HPEM signal. It is then the given task to compute the electric field distribution in the vicinity of the antenna. To this end, a macromodel of the nonlinearly loaded structure that relates the transient signal to the electric field measured at an observation point is derived. As a result it is seen how recent macromodeling techniques can be applied to solve the given problem step by step. This provides the possibility to further analyze the interaction of the given nonlinear loads by a general framework.</p
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