SNR enhancement through phase dependent signal reconstruction algorithms for phase separated interferometric signals

We report several signal reconstruction algorithms for processing phase separated homodyne interferometric signals. Methods that take advantage of the phase of the signal are experimentally shown to achieve a signal-to-noise ratio (SNR) improvement of up to 5 dB over commonly used algorithms. To begin, we present a derivation of the SNR resulting from five image reconstruction algorithms in the context of a 3x3 fiber-coupler based homodyne optical coherence tomography (OCT) system, and clearly show the improvement in SNR associated with phase-based algorithms. Finally, we experimentally verify this improvement and demonstrate the enhancement in contrast and improved image quality afforded by these algorithms through homodyne OCT imaging of a Xenopus laevis tadpole. These algorithms can be generally applied in signal extraction processing where multiple phase separated measurements are available

Integrating a Global Induction Mechanism into a Sequent Calculus

Most interesting proofs in mathematics contain an inductive argument which requires an extension of the LK-calculus to formalize. The most commonly used calculi for induction contain a separate rule or axiom which reduces the valid proof theoretic properties of the calculus. To the best of our knowledge, there are no such calculi which allow cut-elimination to a normal form with the subformula property, i.e. every formula occurring in the proof is a subformula of the end sequent. Proof schemata are a variant of LK-proofs able to simulate induction by linking proofs together. There exists a schematic normal form which has comparable proof theoretic behaviour to normal forms with the subformula property. However, a calculus for the construction of proof schemata does not exist. In this paper, we introduce a calculus for proof schemata and prove soundness and completeness with respect to a fragment of the inductive arguments formalizable in Peano arithmetic.Comment: 16 page

On Exchange of Orbital Angular Momentum Between Twisted Photons and Atomic Electrons

We obtain an expression for the matrix element for a twisted (Laguerre-Gaussian profile) photon scattering from a hydrogen atom. We consider photons incoming with an orbital angular momentum (OAM) of $\ell \hbar$, carried by a factor of $e^{i \ell \phi}$ not present in a plane-wave or pure Gaussian profile beam. The nature of the transfer of $+2\ell$ units of OAM from the photon to the azimuthal atomic quantum number of the atom is investigated. We obtain simple formulae for these OAM flip transitions for elastic forward scattering of twisted photons when the photon wavelength $\lambda$ is large compared with the atomic target size $a$, and small compared the Rayleigh range $z_R$, which characterizes the collimation length of the twisted photon beam.Comment: 16 page

Infrared Emission from the Radio Supernebula in NGC 5253: A Proto-Globular Cluster?

Hidden from optical view in the starburst region of the dwarf galaxy NGC 5253 lies an intense radio source with an unusual spectrum which could be interpreted variously as nebular gas ionized by a young stellar cluster or nonthermal emission from a radio supernova or an AGN. We have obtained 11.7 and 18.7 micron images of this region at the Keck Telescope and find that it is an extremely strong mid-infrared emitter. The infrared to radio flux ratio rules out a supernova and is consistent with an HII region excited by a dense cluster of young stars. This "super nebula" provides at least 15% of the total bolometric luminosity of the galaxy. Its excitation requires 10^5-10^6 stars, giving it the total mass and size (1-2 pc diameter) of a globular cluster. However, its high obscuration, small size, and high gas density all argue that it is very young, no more than a few hundred thousand years old. This may be the youngest globular cluster yet observed.Comment: 6 pages, 2 color figures, Submitted to the ApJL, Revised 4/6/01 based on referee's comment

Decision-making: initiating insulin therapy for adults with diabetes

<b>AIM:</b> This paper is a report of a study to describe nurses' perceptions of decision-making and the evidence base for the initiation of insulin therapy. <b>BACKGROUND:</b> Several theoretical perspectives and professional's attributes underpin decision-making to commence insulin therapy. The management of type 2 diabetes is moving from secondary to primary care and this affects how clinical decisions are made, by whom and the evidence base for these decisions. <b>METHOD:</b> A postal survey was conducted with a stratified sample of 3478 Diabetes Specialist Nurses and Practice Nurses with a special interest in diabetes across the four countries of the United Kingdom. A total of 1310 valid responses were returned, giving a response rate of 37.7%. The questionnaire was designed for the study and pilot-tested before use. Responses were given using Likert-type scales. Data were collected during 2005 and 2006, and one reminder was sent. <b>RESULTS:</b> People with diabetes are seen as having little influence in decision-making. Consultant physicians appear to be influential in most decisions, and the nursing groups held varying perceptions of who made clinical decisions. Nurses' identified different responsibilities for those working solely in secondary care from those working in both community and secondary care. Practice nurses were not as involved as anticipated. <b>CONCLUSION:</b> Nurses working with people with diabetes need to encourage them to become more active partners in care. Clinical guidelines can assist in decision-making where nurses are least experienced in initiating insulin therapy

Glass ceilings and stone floors: an intersectional approach to challenges UK geographers face across the career lifecycle

While there has been a steady growth of women working in geography in UK universities since the mid-Twentieth Century, there are continuing challenges in gendered career progression and professional interactions within the contemporary discipline. These range from problems associated with employment precarity and inflexible work practices, life choices and obligations in the domestic arena, discrimination and bullying, to less tangible gendered norms and cultures in the workplace. This paper discusses these challenges and inequalities in the light of a brief overview of sector-wide statistical data on appointments by gender and career-stage and with the analysis of some 250 in-depth responses to a nationwide qualitative survey of gender and career experience in UK universities (Maddrell et al 2016). While the term ‘glass ceiling’ still has significant relevance, findings show a more complicated picture which also includes ‘stone floors’ and stumbling blocks. It also shows how career experience varies by institution and individual: challenges in career progression can be compounded by institutional protocols and intersectional factors, and vary with career stage. The intersection of early-career job precarity, reproductive decisions and associated family responsibilities were particularly highlighted in this study. These ‘pinch points’ in career development disproportionately affect, but are not limited to, female early career scholars. Early career progress may be stalled in mid-career in multi-staged promotional systems such as that in UK universities; some from minorities face compound barriers; men with caring responsibilities may face prejudice. The paper concludes with suggested strategies for change, highlighting the importance of individual university and department protocols and practices; line manager and other senior colleagues’ attitudes and leadership in creating workplaces with an equality-driven ethos and structures that allow individuals to flourish

Stellar-Mass Black Holes in the Solar Neighborhood

We search for nearby, isolated, accreting, ``stellar-mass'' (3 to $100M_\odot$) black holes. Models suggest a synchrotron spectrum in visible wavelengths and some emission in X-ray wavelengths. Of 3.7 million objects in the Sloan Digital Sky Survey Early Data Release, about 150,000 objects have colors and properties consistent with such a spectrum, and 87 of these objects are X-ray sources from the ROSAT All Sky Survey. Thirty-two of these have been confirmed not to be black-holes using optical spectra. We give the positions and colors of these 55 black-hole candidates, and quantitatively rank them on their likelihood to be black holes. We discuss uncertainties the expected number of sources, and the contribution of blackholes to local dark matter.Comment: Replaced with version accepted by ApJ. 40 pages, 8 figure

Chandra Observations of the Dwarf Nova WX Hyi in Quiescence

We report Chandra observations of the dwarf nova WX Hyi in quiescence. The X-ray spectrum displays strong and narrow emission lines of N, O, Mg, Ne, Si, S and Fe. The various ionization states implied by the lines suggest that the emission is produced within a flow spanning a wide temperature range, from T ~ 10^6 K to T >~ 10^8 K. Line diagnostics indicate that most of the radiation originates from a very dense region, with n ~ 10^{13}-10^{14} cm^{-3}. The Chandra data allow the first tests of specific models proposed in the literature for the X-ray emission in quiescent dwarf novae. We have computed the spectra for a set of models ranging from hot boundary layers, to hot settling flows solutions, to X-ray emitting coronae. WX Hyi differs from other dwarf novae observed at minimum in having much stronger low temperature lines, which prove difficult to fit with existing models, and possibly a very strong, broad O VII line, perhaps produced in a wind moving at a few x 10^3 km/s. The accretion rate inferred from the X-rays is lower than the value inferred from the UV. The presence of high-velocity mass ejection could account for this discrepancy while at the same time explaining the presence of the broad O VII line. If this interpretation is correct, it would provide the first detection of a wind from a dwarf nova in quiescence.Comment: accepted to ApJ; 19 pages, 3 figures, 1 tabl