228 research outputs found

    Artificial three-body equilibria for hybrid low-thrust propulsion

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    This paper proposes a new concept of creating artificial equilibrium points in the circular restricted three body problem, where the third body uses a hybrid of solar sail and solar electric propulsion. The work aims to investigate the use of a hybrid sail for artificial equilibrium points that are technologically di±cult with either of these propulsion systems alone. The hybrid sail has freedom in specifying the sail lightness number, then minimizing the required thrust acceleration from the solar electric propulsion thruster while satisfying the equilibrium condition. The stability analysis of such artificial equilibrium points by a linear method results in a linear time varying (mass) system. The freezing time method then provides unstable and marginally stable regions for hybrid solar sail artificial equilibria. We compare these propulsion systems with a given payload mass and mission life for a polar observation mission. For a near term sail assembly loading we find for the hybrid sail a substantially lower propellant mass compared to solar electric propulsion and lower sail length with respect to a solar sail, and a lower initial spacecraft mass

    Post stroke seizures: descriptive study from a tertiary care centre in Pakistan

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    OBJECTIVE: To determine the frequency, mode of onset and outcome of post stroke seizures in a local setting. METHODS: The retrospective (Aug 1999 to July 2001) and prospective (August 2001 to July 2002) data of patients aged 14 years and above, with post stroke seizures was collected from a tertiary care centre in a metropolitan city. The demographic, clinical, radiological, laboratory, neurophysiologic and outcome data was recorded and analyzed. RESULTS: During the three year period 1548 patients with stroke were admitted to the hospital. Four hundred thirty one (28%) had intracerebral haemorrhage (ICH) and 1117 (72%) had ischaemic stroke. One hundred seventeen (8%) of the 1548 had seizures. Their mean age was 63 +/- 12 (range; 15-70) years. Fifty-nine (50%) were men and 58 (50%) were women. Twenty of 431(5%) patients with ICH and 97/1117 (9%) with ischaemic stroke, developed seizures. Nine of 117 (8%) developed a seizure within 14 days of stroke and 108/117 (92%) developed seizures after 14 days of stroke. Twenty-six (22%) had partial and 91 (78%) had generalized seizures. Two patients expired early in the course. Twenty four (21%) of these continued to have seizures at one year follow up. Fifteen of 37 (40%) patients who had systemic infections early in the course continued to have seizures at one year as compared to 9/80 (11%) who did not (p = 0.001). CONCLUSIONS: Frequency of post stroke seizures is the same as reported in western literature. Post stroke seizures are more common in patients with ischaemic stroke. Generalized seizures are more common than partial seizures. Systemic infections early in the course are associated with recurrence of seizures at one year

    Making rainfed agriculture sustainable through environmental friendly technologies in Pakistan: A review

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    Abstract:Pakistan is an agricultural country spreading over an area of about 79. 6 million hectares (Mha) with an arid and semi arid climate. Of 79. 6 Mha, about 23 Mha is suitable for crop production and nearly 25 percent of the total cultivated area is designated for rainfed agriculture. Unfortunately, rain-fed agriculture is constrained with multifarious problems such as moisture stress, soil erosion and crusting, nutrient deficiency, depletion and poor nutrient use efficiency, and weed infestation limiting the yield potential of these lands. In addition, deforestation and poor crop husbandry techniques are commonly noticed features. To meet the food requirements, farmers bring all the available pieces of lands under plough including steep slopes. Farming on steep slopes if not managed on scientific lines, results in severe erosion. The problems faced by the farmers are due to the unsustainable practices they adopt to practice dryland agriculture, limiting the productive potential of these important ecosystems. However, their potential can be improved by adopting suitable rainwater harvesting techniques; employing scientific soil and water conservation methods and using sustainable agricultural practices. This paper highlights some important issues associated with the rainfed agriculture of Pakistan. Working strategies for realizing optimum and sustainable yields have been outlined while conserving both land and water resources

    Whole exome sequencing identifies a novel mutation in ASPM and ultra-rare mutation in CDK5RAP2 causing primary microcephaly in consanguineous Pakistani families

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    Background & objectives: Primary Microcephaly (MCPH) is a rare neurogenetic disease, manifesting congenitally reduced head circumference and non-progressive intellectual disability (ID). To date, twenty-eight genes with biallelic mutations have been reported for this disorder. The study aimed for molecular genetic characterization of Pakistani families segregating MCPH. Methods: We studied two unrelated consanguineous families (family A and B) presenting \u3e2 patients with diagnostic symptoms of MCPH, born to asymptomatic parents. We employed whole-exome sequencing (WES) of probands to find putative causal mutations. The candidate variants were further confirmed and analyzed for co-segregation by Sanger sequencing of all available members of each family. This study was conducted at Government College University, Faisalabad, Pakistan, and Cologne Center for Genomics (CCG), University of Cologne, Germany; during 2017-2020. Results: We identified a novel homozygous variant c.10097_10098delGA, p.(Gly3366Glufs*19) in exon 26 of ASPM gene in family A which presents with moderate intellectual disability, speech impairment, visual abnormalities, seizures, and ptyalism. Family B was found to segregate nonsense, homozygous variant c.448C\u3eT p.(Arg150*) in CDK5RAP2. The patients also exhibited mild to severe seizures without ptyalism that has not been previously reported in patients with mutations in the CDK5RAP2 gene. Conclusion: We report a novel mutation in ASPM and ultra-rare mutation in the CDK5RAP2 gene, both causing primary microcephaly. The study expands the mutational spectrum of the ASPM gene to 212, and also adds to the clinical spectrum of CDK5RAP2 mutations. It also demonstrated the utility of WES in the investigation and genetic diagnosis of genetically heterogeneous disorders like MCPH. These findings would aid in diagnostic and preventive strategies including carrier screening, cascade testing, and genetic counselling

    Light levitated geostationary cylindrical orbits are feasible

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    This paper discusses a new family of non-Keplerian orbits for solar sail spacecraft displaced above or below the Earth's equatorial plane. The work aims to prove the assertion in the literature that displaced geostationary orbits exist, possibly to increase the number of available slots for geostationary communications satellites. The existence of displaced non-Keplerian periodic orbits is ¯rst shown analytically by linearization of the solar sail dynamics around a geostationary point. The full displaced periodic solution of the non-linear equations of motion is then obtained using a Hermite-Simpson collocation method with inequality path constraints. The initial guess to the collocation method is given by the linearized solution and the inequality path constraints are enforced as a box around the linearized solution. The linear and nonlinear displaced periodic orbits are also obtained for the worst-case Sun-sail orientation at the solstices. Near-term and high-performance sails can be displaced between 10 km and 25 km above the Earth's equatorial plane during the summer solstice, while a perforated sail can be displaced above the usual station-keeping box (75 £ 75 km) of nominal geostationary satellites. Light-levitated orbit applications to Space Solar Power are also considered
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