M. S. Khan

Cloud attenuations for free-space optical links

Free-space Optics (FSO) or optical wireless offers huge unlicensed bandwidth and is able to deliver the required bandwidth needed in next ten years for the next generation networks (NGN). Moreover, an increasing number of military and commercial access systems rely critically on the propagation of optical energy through the atmospheric free-space. As a result the need for predictable estimates of optical attenuation in low visibility conditions is steadily increasing, especially for fog, rain, clouds and snowfall. Cloud attenuations are the least observed/measured in case of free-space optical wireless links. We investigate here the influence of cloud attenuations on the performance of optical wireless links.

Selecting a distribution function for optical attenuation in dense continental fog conditions

Free Space Optics (FSO) is a broadband access technology finding numerous applications in next generation networks (NGN). The biggest disadvantage of this technology is its dependence on local weather conditions in the free-space atmospheric channel. This requires a thorough investigation of different attenuating factors and their influence on FSO transmissions. In this paper we analyze the behavior of dense continental fog on FSO links by investigating different probability distribution functions for measured optical attenuations. Several probability distributions are used; to observe reasonable probability distribution which best suits to describe the characteristics of FSO links under dense continental fog conditions. Further, Kolmogorov-Smirnov non-parametric test is used for goodness of fit of the selected probability distributions. The results of Kolmogorov-Smirnov test suggests that Wakeby probability distribution function is reasonable to describe the behavior of optical attenuation data measured in a dense continental fog environment.

Morphological characterization of Achai cattle in sedentary and transhumant systems in Pakistan

Achai is an as yet undocumented but well-adapted cattle breed of the Hindu Kush Mountains of northern Pakistan, which is reared under sedentary farming system (SFS) and transhumant farming system (TFS). This paper compares the morphological (physical and morphometric) characteristics of this cattle breed under both farming systems to know the effect of these styles of management. Data were collected from 108 adult females and 108 males in SFS and 108 females and 36 males in TFS on physical characteristics (colour of the coat, horns, eyelashes, muzzle, hoof, switch) and morphometric measurements – i.e. heart girth, body length, height at withers, height at hipbone, face length, horn length, horn circumference, ear (length and width), neck length, dewlap length, chine length, loin length, rump (length and width), length below knee, hoof circumference, tail and switch length. Results showed that farming systems significantly affect most of the morphological characteristics of both sexes, particularly the morphometric measurements with tall and leggy conformation for TFS cows and bulls. This indicates an adaptation to long distance transhumance and mountain terrain grazing. It can be concluded that the Achai has the potential to adapt to the requirements of specific farming systems. There is hence a need for the conservation of its adaptive traits in both farming systems.

Optical wireless ground- link attenuation statistics of fog and snow conditions

Optical wireless technology is a well known technology that found renewed interest for its numerous applications in ground-space and terrestrial communication scenarios. A well known disadvantage of optical wireless communication (involving ground-link) is its sensitivity on local weather conditions - primarily to fog, snow and clouds. This results in substantial loss of optical signal power over the communication channel (i.e., the troposphere). We provide here the optical signal attenuation statistics of the fog and snow conditions from an optical wireless ground-link installed at Graz, Austria and provide some useful analysis that can be handful and beneficial in order to evaluate this technology for ground-space future applications.

Effect of management on reproductive performances of the Achai cattle in the Hindu Kush (Northern Pakistan)

This study evaluates the effect of management on the undocumented Achai cattle reproductive performance in transhumant farming systems (TFS) and in sedentary farming systems (SFS) in northwestern Pakistan. Data were collected from 172 households in TFS and 270 households in SFS to analyze the effect of farming systems, parity, and calving season on key reproductive traits. The results show that farming systems significantly affect pubertal age, while parity has no significant effect on any of the key traits. The calving season significantly affects the postpartum anoestrus interval in TFS only. More than 50% of the cows in both systems have postpartum anoestrus intervals and calving intervals within the recommended values for cows in tropical countries. Achai cows have high first-service conception rates (70% and 71% for TFS and SFS, respectively) and require a relatively small number of services per conception (1.53u2009±u20090.06 and 1.48u2009±u20090.05xa0SE for TFS and SFS, respectively). This local breed thus warrants conservation under both farming systems.

Morphological characterization of the Azikheli buffalo in Pakistan

This study aims to characterize Azikheli, an undocumented buffalo breed, in its home tract (Khwazakhela, Swat, Pakistan) under traditional farming conditions. For this purpose, 108 buffalo cows and 27 bulls were randomly selected. Mean, standard error, Students t test and Chi-square test were used for various comparisons. The results show that the majority of animals have a brown coat colour. Cows have significantly higher heart girths, longer horns, longer necks and wider faces at the level of the eyes than bulls, whereas bulls have significantly longer bodies, longer ears, thicker horns, thicker necks and larger hooves than cows. Horns are flat laterally, directed backwards and then slightly upwards without twisting, leading to a sickle to semi-sickle appearance. Owing to its small body size and brown coat colour, the breed is well adapted to mountain slope grazing and thrives well away from swamps. Its adaptation to mountainous ecosystems warrants its in situ conservation.

Mountain cattle breed for coping with climate change: needs for conserving and reintroducing the Achai in the Hindu Kush Mountains of Northern Pakistan

Local low input and output breeds are often a better choice for herders rearing livestock in remote mountains. With more vulnerability to diseases outbreaks and more pasture resources uncertainties as a consequence of climate change, these high resistant and well adapted breeds deserve more attention from local authorities. Local breeds also perform well on poor quality roughages, and can move on rugged terrain for grazing, whereas the exotic and crossbred heavy milk cattle breeds require quality rations, and are more vulnerable to diseases and weather extremes (KOHLER-ROLLEFSON et al., 2009).

Throughput efficient solution for hybrid wireless network

Free Space Optics (FSO) links provide usage of high bandwidth and the flexibility of wireless communication links. However, weather patterns like fog and heavy snow fall limit the availability of FSO. Another technology providing similar properties regarding offered data rates and flexibility of set up is Millimeter Wave Technology (mmW), operating at several tens of GHz. In this case, heavy rain limits mmW link availability. A combination of both technologies has been proved to be very effective to achieve very high availability. This requires redundant transmission on both links, which results in loss of transmission bandwidth. In this paper, a bandwidth efficient switch-over between these technologies is discussed. This switch-over can maintain high availability without the loss of available bandwidth for unnecessary redundant transmission. The performance of this switch-over has been simulated for more than one year measured availability data for hybrid network of mmW link and FSO link. It has been shown that the availability with switch-over reaches the redundant link availability but it can increase the hybrid network throughput significantly.