High Duty Cycle Research Articles

ON THE RADIATIVE EFFICIENCIES, EDDINGTON RATIOS, AND DUTY CYCLES OF LUMINOUS HIGH-REDSHIFT QUASARS

We investigate the characteristic radiative efficiency \epsilon, Eddington ratio \lambda, and duty cycle P_0 of high-redshift active galactic nuclei (AGN), drawing on measurements of the AGN luminosity function at z=3-6 and, especially, on recent measurements of quasar clustering at z=3-4.5 from the Sloan Digital Sky Survey. The free parameters of our models are \epsilon, \lambda, and the normalization, scatter, and redshift evolution of the relation between black hole mass \mbh and halo virial velocity V_vir. We compute the luminosity function from the implied growth of the black hole mass function and the quasar correlation length from the bias of the host halos. We test our adopted formulae for the halo mass function and halo bias against measurements from the large N-body simulation developed by the MICE collaboration. The strong clustering of AGNs observed at z=3 and, especially, at z=4 implies that massive black holes reside in rare, massive dark matter halos. Reproducing the observed luminosity function then requires high efficiency \epsilon and/or low Eddington ratio \lambda, with a lower limit (based on 2\sigma agreement with the measured z=4 correlation length) \epsilon> 0.7\lambda/(1+0.7\lambda), implying \epsilon > 0.17 for \lambda > 0.25. Successful models predict high duty cycles, P_0~0.2, 0.5, and 0.9 at z=3.1, 4.5 and 6, respectively, and they require that the fraction of halo baryons locked in the central black hole is much larger than the locally observed value. The rapid drop in the abundance of the massive and rare host halos at z>7 implies a proportionally rapid decline in the number density of luminous quasars, much stronger than simple extrapolations of the z=3-6 luminosity function would predict. (abridged)

PROCEDURE FOR ASSESSMENT OF GENERAL PUBLIC EXPOSURE FROM WLAN IN OFFICES AND IN WIRELESS SENSOR NETWORK TESTBED

A fast and accurate measurement procedure to determine experimentally wireless local area network (WLAN) radiofrequency (RF) exposure and to test compliance with international guidelines for the general public is proposed. This is the first paper where all optimal settings for the measurement equipment (sweep time, resolution bandwidth, etc.) are investigated, selected, and validated. The exposure to WLAN access points is determined for 222 locations with 7 WLAN networks present in office environments. The WLAN exposure is also characterized for the first time in a wireless sensor lab environment (WiLab) at IBBT-Ghent University in Belgium. Average background exposure to WLAN (WiLab off) is 0.12 V m(-1), with a 95 percentile of 0.90 V m(-1). With the WiLab in operation, average exposure increases to 1.9 V m(-1), with a 95 percentile of 4.7 V m(-1). All values are well below the International Commission on Non Ionizing Radiation Protection guidelines of 61 V m(-1) in the 2.4 GHz band (at least 9.1 times for distances of more than 1 m from the access points) but a significant increase of exposure is possible in WiLabs due to high duty cycles. By applying the proposed measurement method a relevant reduction in measurement time is obtained.

KEPLER OBSERVATIONS OF TRANSITING HOT COMPACT OBJECTS

Kepler photometry has revealed two unusual transiting companions: one orbiting an early A-star and the other orbiting a late B-star. In both cases, the occultation of the companion is deeper than the transit. The occultation and transit with follow-up optical spectroscopy reveal a 9400 K early A-star, KOI-74 (KIC 6889235), with a companion in a 5.2 day orbit with a radius of 0.08 R☉ and a 10,000 K late B-star KOI-81 (KIC 8823868) that has a companion in a 24 day orbit with a radius of 0.2 R☉. We infer a temperature of 12,250 K for KOI-74b and 13,500 K for KOI-81b. We present 43 days of high duty cycle, 30 minute cadence photometry, with models demonstrating the intriguing properties of these objects, and speculate on their nature.

DISCOVERY OF THE TRANSITING PLANET KEPLER-5b

We present 44 days of high duty cycle, ultra precise photometry of the 13th magnitude star Kepler-5 (KIC 8191672, Teff=6300 K, logg=4.1), which exhibits periodic transits with a depth of 0.7%. Detailed modeling of the transit is consistent with a planetary companion with an orbital period of 3.548460+/-0.000032 days and a radius of 1.431+/-0.050 Rj. Follow-up radial velocity measurements with the Keck HIRES spectrograph on 9 separate nights demonstrate that the planet is more than twice as massive as Jupiter with a mass of 2.114+/-0.057 and a mean density of 0.894+/-0.079 g/cm^3.

Polarized GaN-based LED with an integrated multi-layer subwavelength structure

A novel type of GaN-based LED with a highly polarized output using an integrated multi-layer subwavelength grating structure is proposed. Characteristics of both optical transmission and polarization extinction ratio of the polarized GaN-based LED with three different multi-layer subwavelength structures are investigated. It is found that both TM transmission (T(TM)) and the extinction ratio(ER) of the LED output can be effectively enhanced by incorporating a dielectric transition layer between the metal grating and GaN substrate with a lower refractive index than that of the GaN substrate. Flat sensitivity of the T(TM) on the period, duty cycle of the metallic grating, and the wide range of operating wavelength have been achieved in contrast to the conventional sensitive behavior in single-layer metallic grating. Up to 0.75 high duty cycle of the metallic grating can be employed to achieve >60dB ER while T(TM) maintains higher than ~90%, which breaks the conventional limit of T(TM) and ER being always a pair of trade-off parameters. Typical optimized multilayer structures in terms of material, thickness, grating periods and duty cycle using MgF(2) and ZnS, respectively, as the transition layers are obtained. The results provide guidance in designing, optimizing and fabricating the novel integrated GaN-based and polarized photonic devices.

The mini-QSO's contribution to cosmic reionization

By employing an improved simulation of the evolution of black holes (BHs) based on the merger tree of dark matter halos, we explore the relationship between the central BH mass Mbh and velocity dispersion σ* at high redshift z ≥ 6 and quantify the mini-QSO's (with BH mass M = 200 – 105M⊙) contribution to cosmic reionization. The simulation demonstrates how seed BHs migrate onto the MBH-σ* relation by merging with each other and accreting gas at z ≥ 6: 1. The correlation between BHs and their host halos increases as the BHs grow; 2. The slope, i.e. ϕ = d log (Mbh)/d log(σ*) in the relationship, is insensitive to the redshift at z > 6. In agreement with previous work, we find that mini-QSOs' ionizing capability to the Universe lies in the range ∼ 25% – 50% if early miniquasars have extremely high duty cycles, i.e. P(z > 6) ∼ 0.9 – 1.

Magnetic microwires for orthogonal fluxgates electroplated with pulse current

In this contribution we present magnetic microwires electroplated with pulse current (PC), used as core for orthogonal fluxgate. We fabricated microwires with different duty cycle, and we studied their magnetic properties as well as their behaviour when employed for orthogonal fluxgate. We observed that the noise at 1 Hz is minimum when a duty cycle between 60% and 80% is used, whereas it increases for lower duty cycle and microwires electroplated with direct current (DC). On the other hand, wires realized with low duty cycle show much wider linear range than those realized with high duty cycle. Thus, we derive that high duty cycle must be preferred if the orthogonal fluxgate is used in feedback mode (because of the lower noise), whereas for some low-end applications when the sensor is used in open loop we prefer wires electroplated with lower duty cycle (because of the wider linear range).

Gamma-ray astronomy with the ARGO-YBJ experiment

The ARGO-YBJ experiment is an Extensive Air Shower detector which combines high altitude location (Tibet, People's Republic of China, 4300 m a.s.l.) and full coverage with Resistive Plate Counters, resulting in an energy threshold of a few hundred GeV. The large field of view (~2 sr) and high duty cycle allow the continuous monitoring of the Northern sky, searching for unknown sources and unpredictable events, such as flares in blazar emissions or high energy Gamma Ray Bursts. In this paper I will present some results obtained in γ-ray astronomy with the ARGO-YBJ experiment.

Anti-bat tiger moth sounds: Form and function

Abstract The night sky is the venue of an ancient acoustic battle between echolocating bats and their insect prey. Many tiger moths (Lepidoptera: Arctiidae) answer the attack calls of bats with a barrage of high frequency clicks. Some moth species use these clicks for acoustic aposematism and mimicry, and others for sonar jamming, however, most of the work on these defensive functions has been done on individual moth species. We here analyze the diversity of structure in tiger moth sounds from 26 species collected at three locations in North and South America. A principal components analysis of the anti-bat tiger moth sounds reveals that they vary markedly along three axes: (1) frequency, (2) duty cycle (sound production per unit time) and frequency modulation, and (3) modulation cycle (clicks produced during flexion and relaxation of the sound producing tymbal) structure. Tiger moth species appear to cluster into two distinct groups: one with low duty cycle and few clicks per modulation cycle that supports an acoustic aposematism function, and a second with high duty cycle and many clicks per modulation cycle that is consistent with a sonar jamming function. This is the first evidence from a community-level analysis to support multiple functions for tiger moth sounds. We also provide evidence supporting an evolutionary history for the development of these strategies. Furthermore, cross-correlation and spectrogram correlation measurements failed to support a “phantom echo” mechanism underlying sonar jamming, and instead point towards echo interference.

Switched-coupled-inductor DC/DC converters with high voltage conversion ratio

When a low voltage DC power source is used, a DC-DC converter with a high step-up voltage gain is required to raise the voltage to more applicable levels. This is typically achieved by using classical converters driven by pulse width modulation (PWM) waves with extremely high duty cycles. Although theoretically step-up converters can achieve an infinite gain as the duty cycle approaches unity, in reality the gain will peak due to losses in the converter. Increasing the duty cycle beyond this point will only degrade the voltage gain. A solution to this problem is to use a converter that will produce the desired gain at a smaller duty cycle. This paper proposes replacing the inductor in the classical boost converter with a switched-coupled-inductor (SCL) configuration in order to achieve high gains with moderate duty cycles. Mathematical analysis is presented along with selected experimental results to support the theoretical considerations.

SIAMOIS, asteroseismolgy at Dome C after CoRoT

SIAMOIS is a ground-based asteroseismology project, to pursue velocity measurements from the Dome C Concordia station in Antarctica. Dome C appears to be the ideal place for ground-based asteroseismic observations as it is capable of delivering a duty cycle as high as 87% during the three-month long polar night. This high duty cycle, a crucial point for asteroseismology, is comparable to the best space-borne observations. We present the quality of the SIAMOIS project, that yields to its selection as top priority by the working group of ARENA dedicated to “Time series observations from Dome C”. We show that, after CoRoT, SIAMOIS proposes a large scientific case, that extends the pioneering work and great discoveries of CoRoT. We depict a few important ingredients of the project: full automation, space-like philosophy, and compatibility with the current facilities at the Concordia station. SIAMOIS has no real competitor before at least 2016/2017, and can be considered as a pathfinder for many important issues concerning astronomical observations at Dome C.

ARENA Solar Astrophysics Working Group Reporting on Dome C Exceptional Potential for Solar Observations

The ARENA Solar Astrophysics Working Group (WG6) is reviewing the exceptional site conditions prevailing at Dome C/Concordia making it a unique place on Earth for solar observations: excellent seeing, low sky brightness, low water vapour and high duty cycle. These qualities open science programmes which can combine very high resolution, coronagraphy, infrared access, and long time series (continuity). Major objectives accessible are the chromosphere-corona interface at very high resolution, direct magnetic field measurements in the chromosphere (prominences) and in the corona, 2D imaging spectroscopy and waves. A first mid-size facility is proposed and described, AFSIIC (Antarctica Facility for Solar Interferometric Imaging and Coronagraphy), using 3×Ø50 cm off-axis telescopes (1.4 m equivalent telescope) to access these objectives with the proper flux, angular resolution and coronagraphic potential. Support infrastructure and logistics have been studied and are discussed, noticeably a 30 m tower to place the observatory over the very thin surface turbulent layer of Dome C.

On the X-ray properties of sub-mm-selected galaxies

We present an analysis of the X-ray properties of 35 submm galaxies(SMGs) in the CDF-N. Using a sample of robust 850micron-selected galaxies, with accurate positions from Spitzer and/or radio counterparts, we find 16 objects (45+/-8%) with significant X-ray detections in the 2Ms Chandra data. 6 of these SMGs (~17+/-6%) have measured X-ray luminosities or upper limits consistent with those expected based on the far-infrared (FIR) or radio-derived star formation rate (SFR), and hence with the X-rays coming solely from star formation. In another 7 sources (20+/-7%) a dominant AGN contribution to the X-ray emission is required, while in 3 more it is unclear whether stellar process or accretion are responsible. Stacking of the X-ray undetected SMGs reveals a highly significant detection. If due to star formation, this corresponds to an average X-ray derived SFR of ~150 Msun/yr. We deduce that the AGN fraction in SMGs based on X-ray observations is 20-29 (+/-7) %, which is towards the lower limit of previous estimates. Spectral analysis shows that in general the SMGs are not heavily obscured in the X-ray but most of the SMGs classfied as AGN show absorption with N_H in excess of 10^22 cm^-2. Of the secure AGN, the bolometric luminosity appears to be dominated by the AGN in only 3 cases. In ~85% of the SMGs, the X-ray spectrum effectively rules out an AGN contribution that dominates the bolometric emission, even if the AGN is Compton thick. The evidence therefore suggests that intense star formation accounts for both the FIR and X-ray emission in most SMGs. We argue that, rather than having an especially high AGN fraction or duty cycle, SMGs have a high X-ray detection rate at very faint fluxes partly because of their high star formation rates and, in rarer cases, because the submm emission is from an AGN.(abridged)

The ATPase Cycle of the Mitotic Motor CENP-E

We have previously shown that the mitotic motor centrosome protein E (CENP-E) is capable of walking for more than 250 steps on its microtubule track without dissociating. We have examined the kinetics of this molecular motor to see if its enzymology explains this remarkable degree of processivity. We find that like the highly processive transport motor kinesin 1, the enzymatic cycle of CENP-E is characterized by rapid ATP binding, multiple enzymatic turnovers per diffusive encounter, and gating of nucleotide binding. These features endow CENP-E with a high duty cycle, a prerequisite for processivity. However, unlike kinesin 1, neck linker docking in CENP-E is slow, occurring at a rate closer to that for Eg5, a mitotic kinesin that takes only 5-10 steps per processive run. These results suggest that like kinesin 1, features outside of the catalytic domain of CENP-E may also play a role in regulating the processive behavior of this motor.

Compact vibration isolation and suspension for Australian International Gravitational Observatory: Local control system

High performance vibration isolators are required for ground based gravitational wave detectors. To attain very high performance at low frequencies we have developed multistage isolators for the proposed Australian International Gravitational Observatory detector in Australia. New concepts in vibration isolation including self-damping, Euler springs, LaCoste springs, Roberts linkages, and double preisolation require novel sensors and actuators. Double preisolation enables internal feedback to be used to suppress low frequency seismic noise. Multidegree of freedom control systems are required to attain high performance. Here we describe the control components and control systems used to control all degrees of freedom. Feedback forces are injected at the preisolation stages and at the penultimate suspension stage. There is no direct actuation on test masses. A digital local control system hosted on a digital signal processor maintains alignment and position, corrects drifts, and damps the low frequency linear and torsional modes without exciting the very high Q-factor test mass suspension. The control system maintains an optical cavity locked to a laser with a high duty cycle even in the absence of an autoalignment system. An accompanying paper presents the mechanics of the system, and the optical cavity used to determine isolation performance. A feedback method is presented, which is expected to improve the residual motion at 1 Hz by more than one order of magnitude.

Radio detection of cosmic rays in the Pierre Auger Observatory

In small-scale experiments such as CODALEMA and LOPES, radio detection of cosmic rays has demonstrated its potential as a technique for cosmic ray measurements up to the highest energies. Radio detection promises measurements with high duty-cycle, allows a direction reconstruction with very good angular resolution, and provides complementary information on energy and nature of the cosmic ray primaries with respect to particle detectors at ground and fluorescence telescopes. Within the Pierre Auger Observatory, we tackle the technological and scientific challenges for an application of the radio detection technique on large scales. Here, we report on the results obtained so far using the Southern Auger site and the plans for an engineering array of radio detectors covering an area of ∼ 20 km 2 .

Dynamical interactions in a green treefrog chorus.

In southeast Texas male green treefrogs (Hyla cinerea) assemble in dense choruses and call for several hours every night to attract females. The call is a short “quank” lasting about a 100 ms, with a variable call interval of about 400 ms. Individuals call from dense vegetation surrounding the breeding area, occupying positions that range in elevation from water level to several meters above the ground. The high call-rate and duty cycle combined with their three-dimensional spatial distribution present challenging problems for signalers and receivers and for human observers. It is qualitatively apparent that within a large natural chorus, individuals dynamically adjust their calling to avoid overlap with other callers. However, the dynamical interactions and calling strategies have not been quantified. Here, a 15-microphone array was deployed within the breeding site in the vicinity of one group of callers, and the locations and call patterns of individuals were extracted by acoustic beamforming. The results show that an individual pays attention to only a few of the neighboring males and times his calls to avoid call collision. When a collision occurs one of the individuals will delay the subsequent call by approximately half a call interval to avoid further collision.

A 7 ps Jitter 0.053 mm<formula formulatype="inline"> <tex Notation="TeX">$^{2}$</tex></formula> Fast Lock All-Digital DLL With a Wide Range and High Resolution DCC

This paper presents a fast lock all-digital delay-locked loop (ADDLL) with a wide range and high resolution all-digital duty cycle corrector (ADDCC), which achieves low jitter, fast lock time, and accurate 50% duty cycle correction with a clock-synchronized delay (CSD) and time-to-digital converter (TDC) schemes. The ADDLL uses a self-calibration scheme to reduce the phase error and jitter, and a range doubler to double its operating frequency range with a negligible increase in power and area. The ADDCC employs a weighted signal generator to improve a resolution problem at high operating frequencies and a cycle detector to insure a wide operation range. The proposed ADDLL with the ADDCC was fabricated using a 0.18 mum CMOS technology that operates over a wide frequency range from 440 MHz to 1.5 GHz with 15 cycles of maximum lock time. The peak-to-peak jitter is 7 ps at 1.5 GHz with a power consumption of 43 mW and the area is 0.053 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

A Modified Alderman–Grant Coil makes possible an efficient cross-coil probe for high field solid-state NMR of lossy biological samples

The design, construction, and performance of a cross-coil double-resonance probe for solid-state NMR experiments on lossy biological samples at high magnetic fields are described. The outer coil is a Modified Alderman–Grant Coil (MAGC) tuned to the 1H frequency. The inner coil consists of a multi-turn solenoid coil that produces a B 1 field orthogonal to that of the outer coil. This results in a compact nested cross-coil pair with the inner solenoid coil tuned to the low frequency detection channel. This design has several advantages over multiple-tuned solenoid coil probes, since RF heating from the 1H channel is substantially reduced, it can be tuned for samples with a wide range of dielectric constants, and the simplified circuit design and high inductance inner coil provides excellent sensitivity. The utility of this probe is demonstrated on two electrically lossy samples of membrane proteins in phospholipid bilayers (bicelles) that are particularly difficult for conventional NMR probes. The 72-residue polypeptide embedding the transmembrane helices 3 and 4 of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) (residues 194–241) requires a high salt concentration in order to be successfully reconstituted in phospholipid bicelles. A second application is to paramagnetic relaxation enhancement applied to the membrane-bound form of Pf1 coat protein in phospholipid bicelles where the resistance to sample heating enables high duty cycle solid-state NMR experiments to be performed.

Intranight polarization variability in radio-loud and radio-quiet AGN

(Abriged) Intranight polarization variability in AGN has not been studied extensively so far. Studying the variability in polarization makes it possibly to distinguish between different emission mechanisms. Thus it can help answering the question if intranight variability in radio-loud and radio-quiet AGN is of the same or of fundamentally different origin. In this paper we investigate intranight polarization variability in AGN. Our sample consists of 28 AGN at low to moderate redshifts (0.048 < z < 1.036), 12 of which are radio-quiet quasars (RQQs) and 16 are radio-loud blazars. The subsample of blazars consists of eight flat-spectrum radio-quasars (FSRQs) and eight BL Lac objects. We find clear differences between the two samples. A majority of the radio-loud AGN show moderate to high degrees of polarization, more than half of them also show variability in polarization. There seems to be a dividing line for polarization intranight variability at P~5 per cent over which all objects vary in polarization. Only two out of 12 radio-quiet quasars show polarized emission, both at levels of P<1 per cent. The lack of polarization intranight variability in radio-quiet AGN points towards accretion instabilities being the cause for intranight flux variability whereas the high duty cycle of polarization variability in radio-loud objects is more likely caused by instabilities in the jet or changes of physical conditions in the jet plasma.