Bimetric varying speed of light theories and primordial fluctuations

We exhibit a varying speed of light (VSL) theory that implements the recently proposed decaying speed of sound mechanism for generating density fluctuations. We avail ourselves of bimetric VSL theories, where the speed of gravity differs from that of light. We first show that a Dirac-Born-Infeld (DBI) type of $K$-essence has the necessary speed of sound profile to produce (near) scale-invariant fluctuations. We then examine the map between bimetric and $K$-essence models: typically the bi-scalar connecting the two metrics is a $K$-essence field in one of them. Remarkably, the DBI model is found to perturbatively represent the minimal bimetric model, where the bi-scalar is Klein-Gordon in the matter frame. But the full non-perturbative bimetric structure is even simpler: the bi-scalar dynamics should be simply driven by a cosmological constant in the matter frame, balanced by an opposite cosmological constant in the gravity frame. Thus the problem of structure formation receives an elegant and universal solution within bimetric VSL theories, which are known to also solve the flatness and entropy problems and evade a plethora of causality concerns

GRB Afterglows from Anisotropic Jets

Some progenitor models of gamma-ray bursts (GRBs) (e.g., collapsars) may produce anisotropic jets in which the energy per unit solid angle is a power-law function of the angle ($\propto\theta^{-k}$). We calculate light curves and spectra for GRB afterglows when such jets expand either in the interstellar medium or in the wind medium. In particular, we take into account two kinds of wind: one ($n\propto r^{-3/2}$) possibly from a typical red supergiant star and another ($n\propto r^{-2}$) possibly from a Wolf-Rayet star. We find that in each type of medium, one break appears in the late-time afterglow light curve for small $k$ but becomes weaker and smoother as $k$ increases. When $k\ge 2$, the break seems to disappear but the afterglow decays rapidly. Thus, one expects that the emission from expanding, highly anisotropic jets provides a plausible explanation for some rapidly fading afteglows whose light curves have no break. We also present good fits to the optical afterglow light curve of GRB 991208. Finally, we argue that this burst might arise from a highly anisotropic jet expanding in the wind ($n\propto r^{-3/2}$) from a red supergiant to interpret the observed radio-to-optical-band afterglow data (spectrum and light curve).Comment: 12 pages + 10 figures, accepted by Ap

Users' perceptions of domestic windows in Hong Kong: Challenging daylighting-based design regulations

The authors suspected that the contemporary quantified daylight control on window design is insufficient to satisfy the user expectation in Hong Kong. A survey was carried out from December 2007 to June 2008 to study the human-window interactions in high-rise residential buildings in Hong Kong. The result indicated that daylighting is not the dominant factor for domestic window design because of Hong Kong's sociocultural context; other factors such as dining habit, toilet hygiene, views from living room and privacy for bedroom proved to be more important in the users perception. This suggested that the current statutory control may not fulfill or match user expectations. Thus, the window design framework should be a qualitative approach with the understanding of space function and user behavior in the sociocultural context in order to provide for a better living environment. © 2010 Macmillan Publishers Ltd.postprin

Controllable vacuum-induced diffraction of matter-wave superradiance using an all-optical dispersive cavity

Cavity quantum electrodynamics (CQED) has played a central role in demonstrating the fundamental principles of the quantum world, and in particular those of atom-light interactions. Developing fast, dynamical and non-mechanical control over a CQED system is particularly desirable for controlling atomic dynamics and building future quantum networks at high speed. However conventional mirrors do not allow for such flexible and fast controls over their coupling to intracavity atoms mediated by photons. Here we theoretically investigate a novel all-optical CQED system composed of a binary Bose-Einstein condensate (BEC) sandwiched by two atomic ensembles. The highly tunable atomic dispersion of the CQED system enables the medium to act as a versatile, all-optically controlled atomic mirror that can be employed to manipulate the vacuum-induced diffraction of matter-wave superradiance. Our study illustrates a innovative all-optical element of atomtroics and sheds new light on controlling light-matter interactions

Lighting Analysis at Access Zone of Tunnel Entrance of Hong Kong-Zuhai-Macao Bridge (HZMB)

The study aimed to evaluate several shading schemes at access zone of the tunnel entrance of HZMB in order to find the best scenario to increase the user lighting comfort. The study analysed the luminance at the tunnel entrance (L20) and energy saving in the thereshold zone. For these analyses, four shading schemes have been simulated. The schemes were the Original Scheme (Zebra, 50% solid & 50% transparent), Option 1 (Gradation Glass), Option 2 (Perforated Material), and Option 3 (No Shading). The results shows that the Original scheme has the lowest L20 luminance and consequently the highest lighting energy saving. While the Option 3 (No Shading) has the highest L20 luminance and consequently the lowest lighting energy saving

Modeling GRB 050904: Autopsy of a Massive Stellar Explosion at z=6.29

GRB 050904 at redshift z=6.29, discovered and observed by Swift and with spectroscopic redshift from the Subaru telescope, is the first gamma-ray burst to be identified from beyond the epoch of reionization. Since the progenitors of long gamma-ray bursts have been identified as massive stars, this event offers a unique opportunity to investigate star formation environments at this epoch. Apart from its record redshift, the burst is remarkable in two respects: first, it exhibits fast-evolving X-ray and optical flares that peak simultaneously at t~470 s in the observer frame, and may thus originate in the same emission region; and second, its afterglow exhibits an accelerated decay in the near-infrared (NIR) from t~10^4 s to t~3 10^4 s after the burst, coincident with repeated and energetic X-ray flaring activity. We make a complete analysis of available X-ray, NIR, and radio observations, utilizing afterglow models that incorporate a range of physical effects not previously considered for this or any other GRB afterglow, and quantifying our model uncertainties in detail via Markov Chain Monte Carlo analysis. In the process, we explore the possibility that the early optical and X-ray flare is due to synchrotron and inverse Compton emission from the reverse shock regions of the outflow. We suggest that the period of accelerated decay in the NIR may be due to suppression of synchrotron radiation by inverse Compton interaction of X-ray flare photons with electrons in the forward shock; a subsequent interval of slow decay would then be due to a progressive decline in this suppression. The range of acceptable models demonstrates that the kinetic energy and circumburst density of GRB 050904 are well above the typical values found for low-redshift GRBs.Comment: 45 pages, 7 figures, and ApJ accepted. Revised version, minor modifications and 1 extra figur

Quaternion-valued single-phase model for three-phase power system

In this work, a quaternion-valued model is proposed in lieu of the Clarke's α, β transformation to convert three-phase quantities to a hypercomplex single-phase signal. The concatenated signal can be used for harmonic distortion detection in three-phase power systems. In particular, the proposed model maps all the harmonic frequencies into frequencies in the quaternion domain, while the Clarke's transformation-based methods will fail to detect the zero sequence voltages. Based on the quaternion-valued model, the Fourier transform, the minimum variance distortionless response (MVDR) algorithm and the multiple signal classification (MUSIC) algorithm are presented as examples to detect harmonic distortion. Simulations are provided to demonstrate the potentials of this new modeling method

Thermal Performance of Naturally Ventilated Classroom in the Faculty of Engineering Hasanuddin University, Gowa Campus

This study aims to identify the thermal performance of naturally ventilated classrooms of the new campus of Faculty of Engineering, Hasanuddin University in Gowa. The natural ventilation system has three main functions that are to provide healthy air for occupants, to provide thermal comfort to the occupants, and to cool the fabrics in the building interior. Thermal comfort perceived by the user is determined by many factors, including physical, psychological, etc. This research was conducted by using the experimental method with research analysis using CFD (Computational Fluid Dynamics) simulation method. The input parameters in the simulation were obtained through field measurement in the form of room dimension, ventilation open area, and microclimate parameter. The simulation is carried out at maximum open conditions in existing ventilation system with open and closed class door treatment. The simulation treatment of airflow input speeds were 0.25, 0.5, 0.75, and 1 m/s. The results showed that the existing ventilation system of Classroom at Faculty of Engineering (FoE) Hasanuddin University (Unhas) with an opening ratio of 16.59 to 22.76% of the floor area is good enough to flow and distribute comfortable air movement inside the classroom, especially at airflow speeds above 0.5 m/s

Influence of temperature, light and plant growth regulators on germination of black pepper (Piper nigrum L.) seeds

Effects of temperature, light and different concentrations of plant growth regulators on germination of Piper nigrum L. seeds was studied under controlled environmental conditions. Black pepper seeds were placed inPetri dishes with filtration papers and the germination and radical  development followed during eighteen days periods. The seeds generally germinated within six or seven days. There was no difference in percentgermination between dark and light treatments, but the development of radical length was significantly influenced by both light and temperature. Germination was highest at 30°C, but seeds also germinated at 25and 35°C. No germination was observed at low (20°C) and high (40 and 45°C) temperatures. The plant growth regulators enhanced the seeds germination and radical length different degree. The results are consistent with the Piper nigrum L. being recalcitrant species need a certain environment condition to germinate