A New Test of the Einstein Equivalence Principle and the Isotropy of Space

Recent research has established that nonsymmetric gravitation theories like Moffat's NGT predict that a gravitational field singles out an orthogonal pair of polarization states of light that propagate with different phase velocities. We show that a much wider class of nonmetric theories encompassed by the $\chi g$ formalism predict such violations of the Einstein equivalence principle. This gravity-induced birefringence of space implies that propagation through a gravitational field can alter the polarization of light. We use data from polarization measurements of extragalactic sources to constrain birefringence induced by the field of the Galaxy. Our new constraint is $10^8$ times sharper than previous ones.Comment: 21 pages, Latex, 3 Postscript figure

Preface - Personal perspectives in nonlinear science : Looking back, looking forward

Peer reviewedPublisher PD

Coherent absorption and enhanced photoluminescence in thin layers of nanorods

We demonstrate a large light absorptance (80%) in a nanometric layer of quantum dots in rods (QRs) with a thickness of 23 nm. This behavior is explained in terms of the coherent absorption by interference of the light incident at a certain angle onto the very thin QR layer. We exploit this coherent light absorption to enhance the photoluminescent emission from the QRs. Up to a seven- and fivefold enhancement of the photoluminescence is observed for p- and s-polarized incident light, respectively.Comment: Physical Review B 201

Theoretical determination of lifetimes of metastable states in Sc III and Y III

Lifetimes of the first two metastable states in Sc^{2+} and Y^{2+} are determined using the relativistic coupled-cluster theory. There is a considerable interest in studying the electron correlation effects in these ions as though their electronic configurations are similar to the neutral alkali atoms, their structures are very different from the latter. We have made a comparative study of the correlation trends between the above doubly ionized systems with their corresponding neutral and singly ionized iso-electronic systems. The lifetimes of the excited states of these ions are very important in the field of astrophysics, especially for the study of post-main sequence evolution of the cool giant stars.Comment: 13 pages, 1 figure and 5 table

Chandra High Resolution X-ray Spectroscopy of AM Her

We present the results of high resolution spectroscopy of the prototype polar AM Herculis observed with Chandra High Energy Transmission Grating. The X-ray spectrum contains hydrogen-like and helium-like lines of Fe, S, Si, Mg, Ne and O with several Fe L-shell emission lines. The forbidden lines in the spectrum are generally weak whereas the hydrogen-like lines are stronger suggesting that emission from a multi-temperature, collisionally ionized plasma dominates. The helium-like line flux ratios yield a plasma temperature of 2 MK and a plasma density 1 - 9 x10^12 cm^-3, whereas the line flux ratio of Fe XXVI to Fe XXV gives an ionization temperature of 12.4 +1.1 -1.4 keV. We present the differential emission measure distribution of AM Her whose shape is consistent with the volume emission measure obtained by multi-temperature APEC model. The multi-temperature plasma model fit to the average X-ray spectrum indicates the mass of the white dwarf to be ~1.15 M_sun. From phase resolved spectroscopy, we find the line centers of Mg XII, S XVI, resonance line of Fe XXV, and Fe XXVI emission modulated by a few hundred to 1000 km/s from the theoretically expected values indicating bulk motion of ionized matter in the accretion column of AM Her. The observed velocities of Fe XXVI ions are close to the expected shock velocity for a 0.6 M_sun white dwarf. The observed velocity modulation is consistent with that expected from a single pole accreting binary system.Comment: 6 figures, AASTEX style, accepted for publication in Ap

The Equivalence Principle in the Non-baryonic Regime

We consider the empirical validity of the equivalence principle for non-baryonic matter. Working in the context of the TH\epsilon\mu formalism, we evaluate the constraints experiments place on parameters associated with violation of the equivalence principle (EVPs) over as wide a sector of the standard model as possible. Specific examples include new parameter constraints which arise from torsion balance experiments, gravitational red shift, variation of the fine structure constant, time-dilation measurements, and matter/antimatter experiments. We find several new bounds on EVPs in the leptonic and kaon sectors.Comment: 22 pages, late

Cyberbullying among University Students: The Kenyan Experience

Although considerable literature has grown around cyberbullying, there are still only limited studies on this within developing economies, especially African countries. In particular, studies on cyberbullying in Africa have failed to have a direct focus on the prevalence of this phenomenon among students in universities. Not only does cyberbullying have an emotional-social impact, it has ramifications on the learning process as well. This subject remains of utmost relevance within academia, and a number of institutions continue to grapple with its impact. The study reported here is an exploratory investigation of 396 students from one of the private universities within Nairobi, Kenya, which aimed at understanding the prevalence of cyberbullying. The study findings revealed that the highest form of victimization was through the act of deception, in which 75.8% of the respondents indicated someone had lied to them electronically. On the other hand, the highest form of perpetration of cyberbullying was through malice, in which 49.7% of the respondents reported sending a rude message to someone electronically. Further, more male students were more likely to commit acts of cyberbullying compared to their female counterparts. This study confirms the existence of cyberbullying within institutions of higher learning in Kenya, with the possibility of generalizability to other developing economies. The level of prevalence reported in this study appears slightly high in comparison to a majority of the findings from the developed economies. Consequently, we submit that it is imperative that educational systems in Africa and other developing economies put in frameworks to deal with the emerging reality of cyberbullying within institutions of higher learning. Such frameworks should facilitate the implementation of useful strategies to help victims of cyberbullying, and at the same, time offer deterrents to the perpetration of cyberbullying

Curved BPS domain walls and RG flow in five dimensions

We determine, in the context of five-dimensional ${\cal N}=2$ gauged supergravity with vector and hypermultiplets, the conditions under which curved (non Ricci flat) supersymmetric domain wall solutions may exist. These curved BPS domain wall solutions may, in general, be supported by non-constant vector and hyper scalar fields. We establish our results by a careful analysis of the BPS equations as well as of the associated integrability conditions and the equations of motion. We construct an example of a curved BPS solution in a gauged supergravity model with one hypermultiplet. We also discuss the dual description of curved BPS domain walls in terms of RG flows.Comment: 18 pages, LaTeX, 5 figures; added reference

EIT: Solar corona synoptic observations from SOHO with an Extreme-ultraviolet Imaging Telescope

The Extreme-ultraviolet Imaging Telescope (EIT) of SOHO (solar and heliospheric observatory) will provide full disk images in emission lines formed at temperatures that map solar structures ranging from the chromospheric network to the hot magnetically confined plasma in the corona. Images in four narrow bandpasses will be obtained using normal incidence multilayered optics deposited on quadrants of a Ritchey-Chretien telescope. The EIT is capable of providing a uniform one arc second resolution over its entire 50 by 50 arc min field of view. Data from the EIT will be extremely valuable for identifying and interpreting the spatial and temperature fine structures of the solar atmosphere. Temporal analysis will provide information on the stability of these structures and identify dynamical processes. EIT images, issued daily, will provide the global corona context for aid in unifying the investigations and in forming the observing plans for SOHO coronal instruments