Injective and Projective Model Structures on Enriched Diagram Categories

In the enriched setting, the notions of injective and projective model structures on a category of enriched diagrams also make sense. In this paper, we prove the existence of these model structures on enriched diagram categories under local presentability, accessibility, and "acyclicity" conditions, using the methods of lifting model structures from an adjunction introduced by Garner, Hess, Kedziorek, Riehl, and Shipley.Comment: 21 page

Observations of four glitches in the young pulsar J1833-1034 and study of its glitch activity

We present the results from timing observations with the GMRT of the young pulsar J1833-1034, in the galactic supernova remnant G21.5-0.9. We detect the presence of 4 glitches in this pulsar over a period of 5.5 years, making it one of a set of pulsars that show fairly frequent glitches. The glitch amplitudes, characterized by the fractional change of the rotational frequency, range from 1 \times 10^-9 to 7 \times 10^-9, with no evidence for any appreciable relaxation of the rotational frequency after the glitches. The fractional changes observed in the frequency derivative are of the order of 10-5 . We show conclusively that, in spite of having significant timing noise, the sudden irregularities like glitches detected in this pulsar can not be modeled as smooth timing noise. Our timing solution also provides a stable estimate of the second derivative of the pulsar spin-down model, and a plausible value for the braking index of 1.857, which, like the value for other such young pulsars, is much less than the canonical value of 3.0. PSR J1833-1034 appears to belong to a class of pulsars exhibiting fairly frequent occurrence of low amplitude glitches. This is further supported by an estimate of the glitch activity parameter, Ag = 1.53 \times 10^-15 s^-2, which is found to be significantly lower than the trend of glitch activity versus characteristic age (or spin frequency derivative) that a majority of the glitching pulsars follow. We present evidence for a class of such young pulsars, including the Crab, where higher internal temperature of the neutron star could be responsible for the nature of the observed glitch activity.Comment: 10 pages, 16 figures, accepted for publication in MNRA

Impact of housing options to inform the development of the regional spatial strategy

The report summarises work undertaken by Experian for emda to assess the economic impact of the preferred housing option set out in the Regional Spatial Strategy (RSS) and examined alternate scenarios linked to population projections

[Review of] Mark Christian Thompson. Black Fascisms: African American Literature and Culture Between the Wars

In How Bigger Was Born, Richard Wright described the political choice available to young black men like Bigger Thomas as being between communism and fascism. A plethora of recent scholarship from critics like Barbara Foley, James Smethurst, and William Maxwell has articulated the complex relationship between black and red in the first half of the twentieth century. Mark Christian Thompson\u27s Black Fascisms begins to explore the other half of Wright\u27s binary, tracing the uses of fascist ideology in the work of Marcus Garvey, George S. Schuyler, Claude McKay, Zora Neale Hurston, and Richard Wright

The geometry of the double-pulsar system J0737-3039 from systematic intensity variations

The recent discovery of J0737-3039A & B-two pulsars in a highly relativistic orbit around one another - offers an unprecedented opportunity to study the elusive physics of pulsar radio emission. The system contains a rapidly rotating pulsar with a spin period of 22.7 ms and a slow companion with a spin period of 2.77 s, hereafter referred to as 'A' and 'B', respectively. A unique property of the system is that the pulsed radio flux from B increases systematically by almost two orders-of-magnitude during two short portions of each orbit. Here, we describe a geometrical model of the system that simultaneously explains the intensity variations of B and makes definitive and testable predictions for the future evolution of the emission properties of both stars. Our model assumes that B's pulsed radio flux increases when illuminated by emission from A. This model provides constraints on the spin axis orientation and emission geometry of A and predicts that its pulse profile will evolve considerably over the next several years due to geodetic precession until it disappears entirely in 15-20 years

Symptoms of poverty within a group of land reform beneficiaries in the Midlands of KwaZulu-Natal: Analysis and policy recommendations

This study identifies different dimensions of poverty affecting the current and future well-being of households within a community of land reform beneficiaries in the Midlands of KwaZulu-Natal. A census survey of the beneficiary households was conducted in May 2002 to gather data on poverty indicators. Principal Component Analysis was used to construct an index of the standard of housing, which was then combined with variables measuring other symptoms of poverty (income, wealth and health) in a Cluster Analysis of the households. The analysis revealed five clusters representing four distinct groups of poverty; households relatively income and asset rich, households relatively income rich but asset poor, households relatively asset rich but income poor and households with the lowest incomes and assets. While income is an important indicator of current poverty, household wealth (measured in terms of saleable assets) indicates ability to cope with adverse shocks – a key issue as life expectancy is declining and old-age pensioners account for a large share of household income in the survey group. It is concluded that child welfare grants could be increased as pension earnings become less effective in combating the symptoms of poverty in this area. In addition, land reform grants may address poverty more effectively when used to purchase equity in joint ventures with commercial farmers than when used to purchase land that many of the beneficiaries cannot use or transact.Food Security and Poverty,

Observations of three slow glitches in the spin rate of the pulsar B1822-09

Three slow glitches in the rotation rate of the pulsar B1822-09 were revealed over the 1995-2004 interval. The slow glitches observed are characterized by a gradual increase in the rotation frequency with a long timescale of several months, accompanied by a rapid decrease in the magnitude of the frequency first derivative by 1-2 per cent of the initial value and subsequent exponential increase back to its initial value on the same timescale. The cumulative fractional increase in the pulsar rotation rate for the three glitches amounts to Delta_nu/nu ~ 7 10^{-8}.Comment: 11 pages, 3 figures. Accepted for publication in MNRA

The 1997 event in the Crab pulsar revisited

A complex event observed in the radio pulses from the Crab pulsar in 1997 included echoes, a dispersive delay, and large changes in intensity. It is shown that these phenomena were due to refraction at the edge of a plasma cloud in the outer region of the Crab Nebula. Several similar events have been observed, although in less detail. It is suggested that the plasma cloud is in the form of filaments with diameter around 3 x 10^11m and electron density of order 10^4 cm-3Comment: 5 pages 4 figs Accepted by MNRA

Testing Models of Magnetic Field Evolution of Neutron Stars with the Statistical Properties of Their Spin Evolutions

We test models for the evolution of neutron star (NS) magnetic fields (B). Our model for the evolution of the NS spin is taken from an analysis of pulsar timing noise presented by Hobbs et al. (2010). We first test the standard model of a pulsar's magnetosphere in which B does not change with time and magnetic dipole radiation is assumed to dominate the pulsar's spin-down. We find this model fails to predict both the magnitudes and signs of the second derivatives of the spin frequencies ($\ddot{\nu}$). We then construct a phenomenological model of the evolution of $B$, which contains a long term decay (LTD) modulated by short term oscillations (STO); a pulsar's spin is thus modified by its B-evolution. We find that an exponential LTD is not favored by the observed statistical properties of $\ddot{\nu}$ for young pulsars and fails to explain the fact that $\ddot{\nu}$ is negative for roughly half of the old pulsars. A simple power-law LTD can explain all the observed statistical properties of $\ddot{\nu}$. Finally we discuss some physical implications of our results to models of the B-decay of NSs and suggest reliable determination of the true ages of many young NSs is needed, in order to constrain further the physical mechanisms of their B-decay. Our model can be further tested with the measured evolutions of $\dot{\nu}$ and $\ddot{\nu}$ for an individual pulsar; the decay index, oscillation amplitude and period can also be determined this way for the pulsar.Comment: To appear in ApJ. 20 pages, 10 figures, first submitted to ApJ on May 14, 2012; referee comments incorporated and re-submitted; typos corrected and one reference added; additional minor comments from the referee incorporate