Nuclear spin warm-up in bulk n-GaAs

We show that the spin-lattice relaxation in n-type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, that cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, that governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping can be studied and harnessed in much simpler model environment of n-GaAs bulk crystal.Comment: 5 pages, 4 figure

Pharmacogenetics of 6-mercaptopurine and methotrexate in childhood acute lymphoblastic leukemia

Farmakogenomika proučava odnos između genetičkog sklopa individue i njegovog odgovora na lekove i jedan je od stubova personalizovane medicine. Dosadašnji princip lečenja da se standardna doza leka daje svim pacijentima sa istom dijagnozom po unapred utvrđenom protokolu se napušta. Za veliki broj pacijenta ta doza leka često nije efikasna i/ili sigurna za upotrebu. Cilj farmakogenomičkih studija je da identifikuju farmakogenomičke markere, varijacije u genomu koje mogu pouzdano da predvide odgovor na terapiju, što je osnov za individualizaciju terapije. Model sistemi bolesti za analizu farmakogenomičkih markera korišćeni u ovom radu su dečja akutna limfoblastna leukemija (ALL) i reumatoidni artritis (RA). Lečenje ovih bolesti uključuje imunosupresivne i citotoksične lekove 6-merkaptopurin (6-MP), metotreksat (MTX), antibiotik baktrim, antimikotik nistatin, kao i anti-TNF lekove. Genetičke varijacije koje modulišu metaboličke puteve povezane sa ovim lekovima su kandidati za farmakogenomičke markere. Cilj ove studije je da ispita učestalosti genetičkih varijanti u genima TPMT, ITPA, ABCB1, ABCC4, TYMS, MTHFR, SLC19A1, DHFR, TNF i IL-6, kao i da oceni farmakogenomički potencijal ovih varijanti u srpskoj populaciji. Biće ispitana i uloga ovih farmakogenomičkih markera kao faktora rizika za razvoj dečje ALL. Ispitaće se i uticaj terapije održavanja, gde okosnicu terapije čine lekovi 6-MP i MTX, kao i pola i uzrasta dece sa ALL na ekspresiju gena TPMT. Biće funkcionalno okarakterisane varijante u genu TPMT, potencijalni modulatori ekspresije gena TPMT, sa posebnom pažnjom na ulogu VNTR regiona u promotoru gena TPMT. U studiju je bilo uključeno 174 pedijatrijskih ALL pacijenata, 73 RA pacijenata i 104 kontrolnih zdravih ispitanika. Genetičke varijacije u svim gorepomenutim genima su određene metodama baziranim na PCR-u...Pharmacogenomics is focused on exploring the relation between the genomic signature of an individual and their drug response. It is the basis for implementation of personalized medicine. The old-fashioned therapeutic paradigm of »one protocol dose fits all patients with the same diagnosis« is getting abandoned. The standard drug dose is often not efficient and/or safe for many of patients. Pharmacogenomic studies identify pharmacogenomic markers, genomic variations that could reliably predict the drug response, which is the basis for therapy individualization. In order to analyze pharmacogenomic markers, childhood acute lymphoblastic leukemia (ALL) and rheumatoid arthritis (RA) are used as disease model systems. ALL and RA therapy protocols include cytotoxic and immunosuppressive drugs 6-mercaptopurine (6-MP) and methotrexate (MTX), antibiotic bactrim and antimycotic nystatin, as well as anti-TNF drugs. Genetic variations that modulate metabolic pathways related to these drugs are candidate pharmacogenomic markers. The aim of this study is to analyze frequencies of genetic variants in TPMT, ITPA, ABCB1, ABCC4, TYMS, MTHFR, SLC19A1, DHFR, TNF and IL-6 genes in Serbian population and to evaluate the pharmacogenomic potential of these variants. Also, the role of these pharmacogenomic markers as risk factors for development of childhood ALL will be assessed. Influence of the maintenance therapy, which includes 6-MP and MTX as most important drugs, as well as the age and gender of patients will be analyzed in regard to TPMT gene expression. Functional assays will be carried out in order to identify potential modifiers of TPMT expression with a special focus on VNTR region in promoter of TPMT gene. In this study, 174 pediatric ALL patients, 73 RA patients and 104 healthy subjects were enrolled. Genetic variants in above-mentioned genes were detected using PCR-based methodology..

Nuclear spin-lattice relaxation in p-type GaAs

Spin-lattice relaxation of the nuclear spin system in p-type GaAs is studied using a three-stage experimental protocol including optical pumping and measuring the difference of the nuclear spin polarization before and after a dark interval of variable length. This method allows us to measure the spin-lattice relaxation time $T_1$ of optically pumped nuclei "in the dark", that is, in the absence of illumination. The measured $T_1$ values fall into the sub-second time range, being three orders of magnitude shorter than in earlier studied n-type GaAs. The drastic difference is further emphasized by magnetic-field and temperature dependences of $T_1$ in p-GaAs, showing no similarity to those in n-GaAs. This unexpected behavior is explained within a developed theoretical model involving quadrupole relaxation of nuclear spins, which is induced by electric fields within closely spaced donor-acceptor pairs.Comment: 9 pages, 8 figure

Fear and its implications for stock markets

The value of stocks, indices and other assets, are examples of stochastic processes with unpredictable dynamics. In this paper, we discuss asymmetries in short term price movements that can not be associated with a long term positive trend. These empirical asymmetries predict that stock index drops are more common on a relatively short time scale than the corresponding raises. We present several empirical examples of such asymmetries. Furthermore, a simple model featuring occasional short periods of synchronized dropping prices for all stocks constituting the index is introduced with the aim of explaining these facts. The collective negative price movements are imagined triggered by external factors in our society, as well as internal to the economy, that create fear of the future among investors. This is parameterized by a ``fear factor'' defining the frequency of synchronized events. It is demonstrated that such a simple fear factor model can reproduce several empirical facts concerning index asymmetries. It is also pointed out that in its simplest form, the model has certain shortcomings.Comment: 5 pages, 5 figures. Submitted to the Proceedings of Applications of Physics in Financial Analysis 5, Turin 200

Nitrogen Use Efficiency in Tomato (Lycopersicon esculentum L.) and French Bean (Phaseolus vulgaris L.) as Influenced by Coating of Urea with Neem Oil and Graded Levels of Nitrogen

In a pot-culture study, 'Arka Shrestha' tomato and 'Arka Komal' French bean were raised on red sandy-loam to compare urea coated with neem oil (2% w/w, NOCU) and prilled urea (PU) applied at 60, 80 and 100% of recommended N dose. To facilitate direct measurement of N use parameters, urea enriched with 15N (1 atom per cent excess) was used as the source of N. Compared to 'no urea' control, the application of N significantly increased dry matter production, fruit/pod yield as well as the parameters of N use. Prilled urea coated with neem oil (NOCU) was superior to PU in both the crops and produced 21% and 9% higher yield compared to the latter. Increasing the dose of N significantly increased dry matter production, yield and all parameters of N use. However, the interaction effects showed that N applied as NOCU at 80% the of recommended dose produced fruit/pod yield at par with that obtained at 100% of the recommended dose applied as PU in both crops. Corresponding fertilizer utilization achieved was 14.9% and 59.0% when 80% of N was applied as NOCU compared to 11.5% and 30.1 obtained when 100% of N was applied as PU in tomato and French bean, respectively