Spectral and temporal changes associated with flux enhancement in 4U 1626-67

4U 1626-67 is an accretion powered X-ray pulsar that shows remarkably stable X-ray luminosity above hours timescale and gradual intensity variation on a few years timescale. Here we report a significant increase in the X-ray intensity in the long term RXTE-ASM light curve of 4U 1626-67. Similar enhancement in the X-ray flux has also been detected in the Swift-BAT light curve. The increase in the X-ray flux took place over a long period of about 100 days and there appears to be two episodes of flux enhancement. We have investigated the spectral and timing features of 4U 1626-67 during its current state of enhanced flux emission with data obtained from the Proportional Counter Array and the High-Energy X-ray Timing Explorer on board the Rossi X-ray Timing Explorer. The source has entered a new spin-up phase with a spin-up rate of 4.02(5) $\times$ 10$^{-13}$ Hz s$^{-1}$. The present spin-up rate is almost half of the earlier spin-up and spin-down trends. A significant excess in soft X-ray photon emission is observed during the enhanced flux state, which is similar to the energy spectrum obtained during the spin-up era of the pulsar before 1990. We also report detection of a significant broadening in the wings of the 130 mHz peak and a change in the shape of the continuum of the power spectrum.Comment: 7 pages, accepted for publication in MNRAS with minor change

Rapid Stochastic Acceleration of Protons to Energies Above 100~TeV in the Accretion Column Of Hercules X-1

An investigation into the acceleration of protons by scattering off relativistic Alfv\'{e}n waves in the accretion column of Hercules X-1 is presented. The mechanism is shown to achieve mean particle energies of 30~TeV under very reasonable assumptions about the environment, and 250~TeV is available under some circumstances. The highest individual energy attained is almost 1~PeV. The protons emerge in the form of a narrow beam directed at the inner edge of the accretion disk, which is favourable because of the reduced power requirement and presence of target material for gamma-ray production.Comment: 14 pages of uuencoded compressed postscript including 10 figures, accepted by Astroparticle Physics, ADP-AT-94-

Desacetyl-α-melanocyte stimulating hormone and α-melanocyte stimulating hormone are required to regulate energy balance.

OBJECTIVE: Regulation of energy balance depends on pro-opiomelanocortin (POMC)-derived peptides and melanocortin-4 receptor (MC4R). Alpha-melanocyte stimulating hormone (α-MSH) is the predicted natural POMC-derived peptide that regulates energy balance. Desacetyl-α-MSH, the precursor for α-MSH, is present in brain and blood. Desacetyl-α-MSH is considered to be unimportant for regulating energy balance despite being more potent (compared with α-MSH) at activating the appetite-regulating MC4R in vitro. Thus, the physiological role for desacetyl-α-MSH is still unclear. METHODS: We created a novel mouse model to determine whether desacetyl-α-MSH plays a role in regulating energy balance. We engineered a knock in targeted QKQR mutation in the POMC protein cleavage site that blocks the production of both desacetyl-α-MSH and α-MSH from adrenocorticotropin (ACTH1-39). RESULTS: The mutant ACTH1-39 (ACTHQKQR) functions similar to native ACTH1-39 (ACTHKKRR) at the melanocortin 2 receptor (MC2R) in vivo and MC4R in vitro. Male and female homozygous mutant ACTH1-39 (Pomctm1/tm1) mice develop the characteristic melanocortin obesity phenotype. Replacement of either desacetyl-α-MSH or α-MSH over 14 days into Pomctm1/tm1 mouse brain significantly reverses excess body weight and fat mass gained compared to wild type (WT) (Pomcwt/wt) mice. Here, we identify both desacetyl-α-MSH and α-MSH peptides as regulators of energy balance and highlight a previously unappreciated physiological role for desacetyl-α-MSH. CONCLUSIONS: Based on these data we propose that there is potential to exploit the naturally occurring POMC-derived peptides to treat obesity but this relies on first understanding the specific function(s) for desacetyl-α-MSH and α-MSH

Much Ado About Nothing: Several Large-Area Surveys for Radio Pulsars From Arecibo

We report surveyed regions and flux limits for several large-area surveys at 430 MHz for radio pulsars using the 305 m reflector at Arecibo, Puerto Rico. The surveys used integration times between 8 and 67 s and covered a total area of ~515 square degrees. No previously undiscovered pulsars were detected in these regions, although all previously known pulsars were detected. The nondetection of new pulsars places constraints on the population of low-luminosity pulsars and must be taken into account in estimates of the local density of millisecond pulsars

Essays on Inflation Dynamics and Labour Market Frictions.

The inflation equation, more commonly known as the Phillips curve, lies at the heart of modern macroeconomic modeling. This Keynesian relationship between inflation and unemployment discovered by Phillips (1958) soon became widely adopted by policymakers in the 1960’s. However, its empirical shortcomings led to competing theories such as the natural rate hypothesis by Friedman (1968), who alongside Phelps (1967) and Lucas (1972), condemned its implications of money non neutrality. More recently, the specification has adapted to capture nominal inertia led by the New Keynesian school of Fisher (1977) and Taylor (1980), as an answer to the classical result of neutrality. The Phillips curve remains as a relationship of interest to capture the aggregate behaviour of the supply side in the economy, connecting the labour market and the pricing decisions of firms. This Thesis consists of three self contained works, each of which are set out within their own chapter but connected by the employment of the theoretical framework of this inflation equation. They attempt to answer three specific economic questions related to inflation dynamics and labour market frictions. The first analysis concerns itself with the labour market policy of the working hours restriction; specifically with the question of how this labour market policy affects unemployment in the long run. I find weak evidence of a fall in unemployment shortly after the announcement of this policy. Secondly, whether or not one can capture the different characteristics displayed by the labour markets of the US and EU using labour market frictions in the determination of inflation dynamics. Our findings lead us to the conclusion that it is indeed possible to capture these characteristics when analyzing a Phillips curve specified in terms of unemployment. Lastly the question of whether aggregate prices are better represented by controlling for heterogeneity. The results obtained lead us to infer that controlling for heterogeneity of this kind does indeed affect the dynamics of the macro model and does not wash out in the aggregate

Essays on inflation dynamics and labour market frictions

The inflation equation, more commonly known as the Phillips curve, lies at the heart of modern macroeconomic modeling. This Keynesian relationship between inflation and unemployment discovered by Phillips (1958) soon became widely adopted by policymakers in the 1960's. However, its empirical shortcomings led to competing theories such as the natural rate hypothesis by Friedman (1968), who alongside Phelps (1967) and Lucas (1972), condemned its implications of money non neutrality. More recently, the specification has adapted to capture nominal inertia led by the New Keynesian school of Fisher (1977) and Taylor (1980), as an answer to the classical result of neutrality. The Phillips curve remains as a relationship of interest to capture the aggregate behaviour of the supply side in the economy, connecting the labour market and the pricing decisions of firms. This Thesis consists of three self contained works, each of which are set out within their own chapter but connected by the employment of the theoretical framework of this inflation equation. They attempt to answer three specific economic questions related to inflation dynamics and labour market frictions. The first analysis concerns itself with the labour market policy of the working hours restriction; specifically with the question of how this labour market policy affects unemployment in the long run. I find weak evidence of a fall in unemployment shortly after the announcement of this policy. Secondly, whether or not one can capture the different characteristics displayed by the labour markets of the US and EU using labour market frictions in the determination of inflation dynamics. Our findings lead us to the conclusion that it is indeed possible to capture these characteristics when analyzing a Phillips curve specified in terms of unemployment. Lastly the question of whether aggregate prices are better represented by controlling for heterogeneity. The results obtained lead us to infer that controlling for heterogeneity of this kind does indeed affect the dynamics of the macro model and does not wash out in the aggregate.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Essays on Inflation Dynamics and Labour Market Frictions.

The inflation equation, more commonly known as the Phillips curve, lies at the heart of modern macroeconomic modeling. This Keynesian relationship between inflation and unemployment discovered by Phillips (1958) soon became widely adopted by policymakers in the 1960’s. However, its empirical shortcomings led to competing theories such as the natural rate hypothesis by Friedman (1968), who alongside Phelps (1967) and Lucas (1972), condemned its implications of money non neutrality. More recently, the specification has adapted to capture nominal inertia led by the New Keynesian school of Fisher (1977) and Taylor (1980), as an answer to the classical result of neutrality. The Phillips curve remains as a relationship of interest to capture the aggregate behaviour of the supply side in the economy, connecting the labour market and the pricing decisions of firms. This Thesis consists of three self contained works, each of which are set out within their own chapter but connected by the employment of the theoretical framework of this inflation equation. They attempt to answer three specific economic questions related to inflation dynamics and labour market frictions. The first analysis concerns itself with the labour market policy of the working hours restriction; specifically with the question of how this labour market policy affects unemployment in the long run. I find weak evidence of a fall in unemployment shortly after the announcement of this policy. Secondly, whether or not one can capture the different characteristics displayed by the labour markets of the US and EU using labour market frictions in the determination of inflation dynamics. Our findings lead us to the conclusion that it is indeed possible to capture these characteristics when analyzing a Phillips curve specified in terms of unemployment. Lastly the question of whether aggregate prices are better represented by controlling for heterogeneity. The results obtained lead us to infer that controlling for heterogeneity of this kind does indeed affect the dynamics of the macro model and does not wash out in the aggregate

A New Keynesian Model with Heterogeneous Price Setting

The Calvo contract pricing mechanism has become the most widely accepted microfoundation to the NK Phillips curve but unfortunately predicts that all firms in the economy face the same probability of price change. To better explain the stylized fact this paper relaxes the homogeneous firm assumption in the Calvo contract, to provide a macroeconomic explanation more consistent with recently available microeconomic evidence that suggests firms face differing probabilities of price change. A simple New Keynesian dynamic stochastic general equilibrium (DSGE) model with nominal rigidities and habit in consumption for the US is estimated using Bayesian techniques and finds evidence of a flexible price sector of around 6% and a sticky price sector of between 55% and 70% depending on model specification.