Acetylcholinesterase-Positive Langerhans Cells in the Epidermis and Wool Follicles of the Sheep

Dendritic acetycholinesterase-positive cells in the basal layer of the epidermis and in wool follicles of the sheep have been identified ultrastructurally as Langerhans cells using a copper ferrocyanide technique to demonstrate acetycholinesterase. This enzyme is located on the outer surface of the plasma membranes of the Langerhans cells and in the intercellular spaces between these cells and the adjacent epithelial cells. No enzyme activity has been detected within Langerhans cells.Langerhans cells in fetal and adult sheep are morphologically similar and no developmental stages have been detected. Ultrastructurally these cells are similar to those described in other mammals. However, in sheep epidermis they are restricted to the basal layer and are less frequent than in man or guinea pig where they are mainly found in the spinous layer. Langerhans cells in the sheep, which form a system in contact with all keratinocytes in the basal layer, may have a significant influence on the function of the epidermis

Loan products to manage liquidity stress when broad-based black empowerment enterprises invest in productive assets

Investments in productive assets by broad-based black economic empowerment (BEE) enterprises in South Africa (SA) during the 1990s have been constrained, in part, by a lack of access to capital. Even if capital can be sourced, BEE businesses often face a liquidity problem, as conventional, equally amortized loan repayment plans do not take into account the size and timing of investment returns, or there are lags in the adjustment of management to such new investments. This paper describes five alternative loan products to the conventional equally amortized loan: the single payment non-amortized loan; the decreasing payment loan; the partial payment loan; the graduated payment loan; and the deferred payment loan. Recent SA experience with the graduated payment loan and the deferred payment loan suggests that there is scope to alleviate the liquidity problem if a wholesaler of funds can offer such terms to private banks and venture capital investors who then on-lend to finance BEE asset investments that are otherwise considered relatively high credit risks. This would shift the liquidity problem away from the client to the wholesaler of the funds, but requires access to capital at favourable interest rates. Such capital could be sourced from empowerment funds earmarked by the private sector, donors and government.Financial Economics,

Determinants of the demand for regular farm labour in South Africa, 1960-2002

This paper estimates long-run price (wage) elasticities of demand for regular farm labour in South Africa using both Ordinary Least Squares (OLS) regression and a Two-stage Least Squares (2SLS) simultaneous-equation model for the period 1960-2002. Both models include a piecewise interactive slope dummy variable with 1991 as the threshold year to reflect South African (SA) commercial farmers’ expectations that farm labour costs would increase as new labour legislation was introduced from the early 1990s onwards. The long-run price (wage) elasticity of demand for regular farm labour in South Africa during 1960-1990 was estimated as -0.25 for OLS and -0.23 for 2SLS regression, respectively. For the period 1991-2002, this elasticity estimate rose to -1.32 and -1.34 for OLS and 2SLS regression, respectively. These results suggest that a marked structural decline in the demand for regular labour has occurred since 1991 that raises questions about the appropriateness of labour laws and minimum wage legislation that have increased the cost of regular farm labour in South Africa.Regular farm labour, SA agriculture, price (wage) elasticities of demand, Farm Management, Labor and Human Capital,

Contribution of pulsars to the gamma-ray background and their observation with the space telescopes GLAST and AGILE

Luminosities and uxes of the expected population of galactic gamma-ray pulsars become foreseeable if physical distributions at birth and evolutive history are assigned. In this work we estimate the contribution of pulsar uxes to the gamma-ray background, which has been measured by the EGRET experiment on board of the CGRO. For pulsar luminosities we select some of the most important gamma-ray emission models, taking into account both polar cap and outer gap scenarios. We nd that this contribution strongly depends upon controversial neutron star birth properties. A comparison between our simulation results and EGRET data is presented for each model, nding an average contribution of about 10%. In addition, we perform the calculation of the number of new gamma-ray pulsars detectable by GLAST and AGILE, showing a remarkable di erence between the two classes of models. Finally, we suggest some improvements in the numerical code, including more sophisticated galactic m odels and di erent populations of pulsars like binaries, milliseconds, anomalous pulsars and magnetars.Comment: 6 pages, 6 figures, to be published in the Proceedings of the 6th International Symposium ''Frontiers of Fundamental and Computational Physics'' (FFP6), Udine (Italy), Sep. 26-29, 200

Two decades of pulsar timing of Vela

Pulsar timing at the Mt Pleasant observatory has focused on Vela, which can be tracked for 18 hours of the day. These nearly continuous timing records extend over 24 years allowing a greater insight into details of timing noise, micro glitches and other more exotic effects. In particular we report the glitch parameters of the 2004 event, along with the reconfirmation that the spin up for the Vela pulsar occurs instantaneously to the accuracy of the data. This places a lower limit of about 30 seconds for the acceleration of the pulsar to the new rotational frequency. We also confirm of the low braking index for Vela, and the continued fall in the DM for this pulsar.Comment: Isolated Neutron Stars conference, London, April 24-28 200

Recent glitches detected in the Crab pulsar

From 2000 to 2010, monitoring of radio emission from the Crab pulsar at Xinjiang Observatory detected a total of nine glitches. The occurrence of glitches appears to be a random process as described by previous researches. A persistent change in pulse frequency and pulse frequency derivative after each glitch was found. There is no obvious correlation between glitch sizes and the time since last glitch. For these glitches $\Delta\nu_{p}$ and $\Delta\dot{\nu}_{p}$ span two orders of magnitude. The pulsar suffered the largest frequency jump ever seen on MJD 53067.1. The size of the glitch is $\sim$ 6.8 $\times 10^{-6}$ Hz, $\sim$ 3.5 times that of the glitch occured in 1989 glitch, with a very large permanent changes in frequency and pulse frequency derivative and followed by a decay with time constant $\sim$ 21 days. The braking index presents significant changes. We attribute this variation to a varying particle wind strength which may be caused by glitch activities. We discuss the properties of detected glitches in Crab pulsar and compare them with glitches in the Vela pulsar.Comment: Accepted for publication in Astrophysics & Space Scienc

Pulsar Timing at Urumqi Astronomical Observatory: Observing System and Results

A pulsar timing system has been operating in the 18-cm band at the Urumqi Astronomical Observatory 25-m telescope since mid-1999. Frequency resolution allowing dedispersion of the pulsar signals is provided by a 2X128X2.5 MHz filterbank/digitiser system. Observations of 74 pulsars over more than 12 months have resulted in updated pulsar periods and period derivatives, as well as improved positions. Comparison with previous measurements showed that the changes in period and period derivative tend to have the same sign and to be correlated in amplitude. A model based on unseen glitches gives a good explanation of the observed changes, suggesting that long-term fluctuations in period and period derivatives are dominated by glitches. In 2000 July, we detected a glitch of relative amplitude Delta_nu/nu~24X1e-9 in the Crab pulsar. The post-glitch decay appears similar to other large Crab glitches.Comment: 11 pages, 9 figures, 4 tables, accepted by MNRA

Influences of neutron star parameters on evolutions of different types of pulsar; evolutions of anomalous X-ray pulsars, soft gamma repeaters and dim isolated thermal neutron stars on the P-\.{P} diagram

Influences of the mass, moment of inertia, rotation, absence of stability in the atmosphere and some other parameters of neutron stars on the evolution of pulsars are examined. It is shown that the locations and evolutions of soft gamma repeaters, anomalous X-ray pulsars and other types of pulsar on the period versus period derivative diagram can be explained adopting values of B$<10^{14}$ G for these objects. This approach gives the possibility to explain many properties of different types of pulsar.Comment: 18 pages, 1 figur

Precision Timing Measurements of PSR J1012+5307

We present results and applications of high precision timing measurements of the millisecond pulsar J1012+5307. Combining our radio observations with results based on optical observations, we derive complete 3-D velocity information for this system. Correcting for Doppler effects, we derive the intrinsic spin parameters of this pulsar and a characteristic age of 8.6 +/- 1.9 Gyr. Our upper limit for the orbital eccentricity of only 8 * 10^-7 (68% C.L.) is the smallest ever measured for a binary system. We demonstrate that this makes the pulsar an ideal laboratory to test certain aspects of alternative theories of gravitation. Our precise measurements suggest deviations from a simple pulsar spin-down timing model, which are consistent with timing noise and the extrapolation of the known behaviour of slowly rotating pulsars.Comment: 9 pages, 6 figure