A survey of nulling pulsars using the Giant Meterwave Radio Telescope

Several pulsars show sudden cessation of pulsed emission, which is known as pulsar nulling. In this paper, the nulling behaviour of 15 pulsars is presented. The nulling fractions of these pulsars, along with the degree of reduction in the pulse energy during the null phase, are reported for these pulsars. A quasi-periodic null-burst pattern is reported for PSR J1738-2330. The distributions of lengths of the null and the burst phases as well as the typical nulling time scales are estimated for eight strong pulsars. The nulling pattern of four pulsars with similar nulling fraction are found to be different from each other, suggesting that the fraction of null pulses does not quantify the nulling behaviour of a pulsar in full detail. Analysis of these distributions also indicate that while the null and the burst pulses occur in groups, the underlying distribution of the interval between a transition from the null to the burst phase and vice verse appears to be similar to that of a stochastic Poisson point process.Comment: 10 pages, 7 figures, accepted for publication in MNRA

Solving fluid dynamics problems with Matlab

MATLAB (short for Matrix Laboratory) was created by Cleve Moler and Jack Little in the 1970’s. It is a programming language for technical computing. Its environment is easy to work with, the syntax is very simple and intuitive, it has powerful toolboxes to treat many different problems in engineering, and it allows us to produce fantastic graphics as the programme runs. It also allows us to create a graphical interface (via graphical user interfaces - GUIs) that gives our programme a look that is very close to professional software. Because of many of the mentioned features, a MATLAB code can be very compact, allowing anyone to have "the big picture" of any code without have to look at all its details. Another great advantage of Matlab is that, if the code is written in a vectorized form, the code can run much faster than if it was written in the traditional form (’a la C/fortran’). The fact that MATLAB allows us to use a powerful toolbox for sparse matrices, is also a great advantage since, many traditional linear algebra operations can be highly improved, allowing the codes to run much faster than it would run with the traditional linear algebra functions. In our work we have made extensive use of MATLAB to do ’proof of concept’ studies, especially when developing new algorithms and techniques for solving systems of coupled nonlinear partial differential equations, such as those which arise in fluid dynamics. This includes, for instance, codes for investigating instabilities in lid-driven cavities, Boppana and Gajjar (2010), instabilities in flow past circular cylinders, Boppana and Gajjar (2011), and transonic flow past aerofoils Pereira and Gajjar (2010). In some cases MATLAB is used in its own right for solving small problems, but the fact that MATLAB is an interpreted language means that for increasing problem sizes, the MATLAB version of the code can be much slower than equivalent versions in other languages especially when one is dealing with very large sparse matrices. On the other hand the beauty of MATLAB is that much of the hard work is buried in the simple syntax and hidden from the user. An example of this is the use of the backslash operator for solving linear systems. Whether the system is sparse or full, the manner in which the equations are solved is hidden from the user and this greatly facilitates code development. In the equivalent fortran versions of the code the replacement for the ’\’ operation requires considerable work and the code translation process is no longer a trivial exercise. In this chapter we will discuss the use of hybrid spectral methods to solve two and three-dimensional problems using MATLAB. There is an excellent book by Trefethen (2000) which discusses the application of spectral methods using MATLAB to solve ordinary and partial differential equations, and which provides the foundation for the techniques described below. To motivate the ideas we first consider the solution of a model elliptic equation of the form a(x, y)ψxx + b(x, y)ψyy + c(x, y)ψx + e(x, y)ψy + f (x, y)ψ = g(x, y), say with Dirichlet boundary conditions in a rectangular domain. To obtain a numerical solution to this problem the first step is to choose an appropriate method and discretization. In our work we have used a combination of spectral methods in one or two dimensions and high order finite difference methods in another dimension. The main reasons for this choice are that a hybrid approach combines the accuracy of spectral methods together with flexibility in comparison to using spectral methods on their own. One restriction with the use of spectral methods is that one needs to use somewhat simplified geometries. A hybrid approach gives more flexibility in this respect. Another important reason stems from consideration of the type of matrix patterns which arise. With finite differences in say the x direction and spectral collocation in the y direction, the coefficient matrix with the unknowns ordered in terms of increasing y values for a fixed x value, has a particular sparsity pattern dependent on the order of the finite-differencing used. Second order finite-differencing leads to a a block tridiagonal matrix whilst with fourth-order finite differences, the matrix is block-pentadiagonal of the form: AqΨq−2 + BqΨq−1 + CqΨq + DqΨq+1 + EqΨq+2 = Rq, q = 0, 1, ...,M. (1) Here Ψq is the vector of unknowns at location x = xq, M+1 is typically the number of points in the x direction and the block matrices are of size N +1 by N +1 where N +1 spectral points are used. UsingMATLAB it is not too difficult to generate a short code to solve the above discrete system and the book by Trefethen (2000) gives plenty of such examples. The problem becomes more challenging when N and M become large, as for example in some fluid flow applications where large N,M values are needed to resolve regions of the flow where the solution changes very rapidly. When using a large number of points the sparse matrix facilities of MATLAB come into their own. The whole coefficient matrix does not need to be stored and by declaring this as a sparse matrix, only the non-zero entries of the block matrices are calculated. This avoids having to store a very large and sparse matrix which can quickly lead to memory problems. Increasing the order of the scheme leads to increased bandwidths. This sparsity pattern can be exploited for 2nd, 4th or even 6th finite-differencing with a direct solver. However, with spectral methods in two directions, unless the differential operator involved has a special form, it is not immediately possible to utilize the sparse nature of the matrix. Whilst this does not pose any intrinsic difficulties if one is coding in MATLAB, with increased number of points the solution phase can become very memory intensive and requires a lot of processor time. The use of the hybrid approach in our work is motivated in part by the observation that the sparse matrix structure can be exploited to write efficient solvers, which not only work well with MATLAB, but can be coded directly in other languages. MATLAB provides for an excellent environment in which one can test and develop solvers of this type. The above techniques have been successfully applied to investigate a whole range of different flow problems governed by the Navier-Stokes and related equations. In the first example we consider the onset of instability in the lid-driven cavity flow. MATLAB was used to generate results on coarse grids and do preliminary eigenvalue computations. For very fine grids, the computations were performed in Fortran 95. The problem is described in detail in Boppana and Gajjar (2010). The second problem concerns the onset of instability in the flow past a row of circular cylinders. Again the same technqiues have been used but for a more complicated geometry. This problem is described in detail in Boppana and Gajjar (2011). The third problem we discuss concerns the inviscid transonic flows past thin airfoils. Here the governing equations are nonlinear and of mixed type and the flow can contain shock wave discontinuities for certain parameter values. The full details are given in Pereira and Gajjar (2010). The same methods as described above are used except now type differencing needs to be incorporated to allow for the different flow behaviours in regions of subsonic and supersonic flow. The method is fast and very robust and we are able to compute steady flows with strong shocks. The code was written in MATLAB, using vectorization when possible, and, in order to produce a good interface with the user, we used GUIs (graphical user interfaces) from MATLAB. The result was a fast and accurate code, with the extra bonus of a very good interface with the user, without a lot of effort in terms of programming. The fact that graphical results can be shown immediately, saves us a lot of work, both on the analysis of the results and on its presentation

Approaches to Preparing Rhodamine-Dyed Monolithic Silica Aerogels

Silica aerogels are unique nanoporous materials that can be used in a variety of applications. Silica aerogels are attractive for window applications as they are monolithic, thermally insulating, and extremely lightweight. They also can be made transparent or translucent. Aerogels can be made using a variety of methods; in this work, a rapid supercritical extraction method (RSCE) is employed. Although typically translucent, silica aerogels can have dyes incorporated within them to create aerogels of a variety of colors. We are investigating the usage of dyed monolithic silica aerogels in window applications to improve aesthetic effects. However, the high temperatures and pressures required for the RSCE process can lead to dye degradation. In this presentation, we demonstrate how to incorporate Rhodamine 6B, Rhodamine B, and Fluorescein into monolithic silica aerogels. Rhodamine B experiences thermal degradation during monolithic aerogel synthesis. Adjusting processing parameters, including temperature and pressure, can minimize thermal degradation while ensuring the structural integrity of the aerogel. Ultraviolet radiation can also lead to dye degradation, which would be problematic for aerogels in a window application. Future work will focus on spectroscopic characterization of the dyed aerogel monoliths

A NANOSCALE DENDRITIC MACROMOLECULES BASED ON ETHANE 1,2-DIAMINE AS POTENTIAL DRUG CARRIERS FOR NSAIDS: SYNTHESIS, CHARACTERIZATION AND APPLICATIONS

Objective: The present work deals with the objective of development and characterization of novel dendritic macromolecules as solubility enhancer and carrier for sustained release of Ketoprofen. Cytotoxicity and hemolytic assay of dendritic macromolecules were also estimated as an objective to evaluate its toxicity and biocompatibility. Methods: Dendritic macromolecules were synthesized using divergent method. Synthesized macromolecules were characterized by spectral techniques such as FTIR, 1H-NMR, 13C-NMR electro-spray ionization mass spectrometry and elemental analysis. Enhanced aqueous solubility of ketoprofen was evaluated with respect to pH, generation number and concentration of dendrimer using Higuchi and Connors method. Sustained release of ketoprofen from ketoprofen loaded dendrimers was measured and compared with that of free ketoprofen. Hemolytic assay and cytotoxicity of G3 dendrimer on A-549 cell lines were studied to evaluate toxicity and biocompatibility of dendrimer. All dendritic macromolecules were fully characterized by spectral techniques. Results: Solubility study revealed that aqueous solubility of ketoprofen by dendrimer increased with increase in pH, concentration and generation of dendrimer. Ketoprofen was released slowly from ketoprofen loaded dendrimer compared to that of free ketoprofen. Dendritic macromolecules were less cytotoxic and showed less hemolytic potential. Conclusion: It can be concluded that dendrimer have high potential as carriers and solubility enhancers of hydrophobic drug. Keywords: Triazine based dendrimer, Ketoprofen, Drug Carrier, Cytotoxicity, Hemolysis

NOVEL HYDROXYL TERMINATED DENDRIMERS AS POTENTIAL DRUG CARRIERS: SUSTAINED RELEASE, HEMOLYSIS AND CYTOTOXICITY STUDY

Objective: Potential of novel hydroxyl terminated dendrimer generations G1(OH)8, G2(OH)32 and G3(OH)128 as solubility enhancers of model drug ketoprofen was evaluated. G3(OH)128 dendrimer was further explored as the novel carrier for sustained release of ketoprofen. Cytotoxicity and hemolytic potential of G3(OH)128 dendrimer were studied to evaluate toxicity of dendrimer. Methods: Higuchi and Connors method was employed to evaluate improved solubility of ketoprofen at different pH and dendrimer generation. Ketoprofen was loaded into G3(OH)128 dendrimer by inclusion complex method. Ketoprofen loaded dendrimer was characterized by Flourier Transform infrared spectroscopy. Sustained release of ketoprofen from ketoprofen loaded dendrimers was studied and compared to that of free ketoprofen. Cytotoxicity of dendrimers on A-549 cell lines were studied by MTT assay technique. Hemolytic potential of G3 dendrimer was also studied. Results: Solubility of practically insoluble ketoprofen was improved up to 0.77-4.89 mg/ml by dendrimer generations. Solubility of ketoprofen was increased with increase in pH, concentrationand generation number of dendrimer. Ketoprofen was released relatively slowly from ketoprofen loaded dendrimer compared to free ketoprofen. Cytotoxicity and hemolytic assay revealed that dendrimers were less toxic compared to PAMAM dendrimers. Conclusion: Improved solubility of ketoprofen by dendrimer generations, its slow release from G3(OH)128 dendrimer and cytotoxicity and hemolytic assay showed dendrimers have potential as drug carriers. Keywords: Triazine Based Dendrimer, Sustained Release, Cytotoxicity, Hemolysis, Ketoprofen, Encapsulation

Sulfur Metabolism Actively Promotes Initiation of Cell Division in Yeast

BACKGROUND:Sulfur metabolism is required for initiation of cell division, but whether or not it can actively promote cell division remains unknown. METHODOLOGY/PRINCIPAL FINDINGS:Here we show that yeast cells with more mtDNA have an expanded reductive phase of their metabolic cycle and an increased sulfur metabolic flux. We also show that in wild type cells manipulations of sulfur metabolic flux phenocopy the enhanced growth rate of cells with more mtDNA. Furthermore, introduction of a hyperactive cystathionine-beta-synthase (CBS) allele in wild type cells accelerates initiation of DNA replication. CONCLUSIONS/SIGNIFICANCE:Our results reveal a novel connection between a key sulfur metabolic enzyme, CBS, and the cell cycle. Since the analogous hyperactive CBS allele in human CBS suppresses other disease-causing CBS mutations, our findings may be relevant for human pathology. Taken together, our results demonstrate the importance of sulfur metabolism in actively promoting initiation of cell division

Salvageability of renal function following renal revascularisation in children with Takayasu’s arteritis-induced renal artery stenosis

Background. Renal artery revascularisation procedures are usually carried out on children with renal artery stenosis from varied causes, including Takayasu’s   arteritis. Reports on the outcome of such procedures in children usually refer to the improvement in blood pressure, with only minimal mention of effects on renal  function.Objective. Salvageability renal function in children who underw ent renal  revascularisation for Takayasu’s arteritis-induced renal artery stenosis (TARAS) was the focus of this study.Methods. We undertook a retrospective analysis of children aged ≤16 years with angiographically confirmed TARAS who underwent renal artery revascularisation procedures between 1990 and 2010. Outcomes of renal function were studied over a period of 2 years and were defined as: (i) improvement: >20% increase in estimated glomerular filtration rate (e-GFR) from presurgery value; (ii) stabilisation: e-GFR within 20% of presurgery value; and (iii) failure: >20% deterioration in e-GFR from presurgery value. The GFR was estimated using the Schwartz formula.Results. Twenty children (9 males and 11 females, age range 2 - 14 years) had 27 renal artery revascularisation procedures. Thirteen of the patients (65.0%) had bilateral renal artery stenosis. The baseline mean e-GFR was 88.6 (standard deviation (SD) 25.4) mL/min/1.73 m2 and the mean duration of follow-up was 28.80 (SD 25.62) months. All the patients had stable or improved renal function until the 2-year follow-up, when the proportion decreased to 92.3% (12/13), as failure was recorded in one child. Bilateral revascularisation was found to be significantly associated with improvement in renal function in the early postoperative period  (p=0.04).Conclusion. Renal artery revascularisation procedures are successful in salvaging renal function in children with TARA

A molecular biology and phase II trial of lapatinib in children with refractory CNS malignancies: a pediatric brain tumor consortium study.

High expression of ERBB2 has been reported in medulloblastoma and ependymoma; EGFR is amplified and over-expressed in brainstem glioma suggesting these proteins as potential therapeutic targets. We conducted a molecular biology (MB) and phase II study to estimate inhibition of tumor ERBB signaling and sustained responses by lapatinib in children with recurrent CNS malignancies. In the MB study, patients with recurrent medulloblastoma, ependymoma, and high-grade glioma (HGG) undergoing resection were stratified and randomized to pre-resection treatment with lapatinib 900 mg/m(2) dose bid for 7-14 days or no treatment. Western blot analysis of ERBB expression and pathway activity in fresh tumor obtained at surgery estimated ERBB receptor signaling inhibition in vivo. Drug concentration was simultaneously assessed in tumor and plasma. In the phase II study, patients, stratified by histology, received lapatinib continuously, to assess sustained response. Eight patients, on the MB trial (four medulloblastomas, four ependymomas), received a median of two courses (range 1-6+). No intratumoral target inhibition by lapatinib was noted in any patient. Tumor-to-plasma ratios of lapatinib were 10-20 %. In the 34 patients (14 MB, 10 HGG, 10 ependymoma) in the phase II study, lapatinib was well-tolerated at 900 mg/m(2) dose bid. The median number of courses in the phase II trial was two (range 1-12). Seven patients (three medulloblastoma, four ependymoma) remained on therapy for at least four courses range (4-26). Lapatinib was well-tolerated in children with recurrent or CNS malignancies, but did not inhibit target in tumor and had little single agent activity.Fil: Fouladi, Maryam. St. Jude Children’s Research Hospital; Estados UnidosFil: Stewart, Clinton F.. St. Jude Children’s Research Hospital; Estados UnidosFil: Blaney, Susan M.. Baylor College of Medicine. Texas Children’s Cancer Center; Estados UnidosFil: Onar Thomas, Arzu. St. Jude Children’s Research Hospital; Estados UnidosFil: Schaiquevich, Paula Susana. St. Jude Children’s Research Hospital; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Packer, Roger J.. Children’s National Medical Center; Estados UnidosFil: Goldman, Stewart. Anne and Robert H. Lurie Children’s Hospital of Chicago; Estados UnidosFil: Geyer, J. Rusell. Children’s Hospital and Regional Medical Center; Estados UnidosFil: Gajjar, Amar. St. Jude Children’s Research Hospital; Estados UnidosFil: Kun, Larry E.. St. Jude Children’s Research Hospital; Estados UnidosFil: Boyett, James M.. St. Jude Children’s Research Hospital; Estados UnidosFil: Gilbertson, Richard J.. St. Jude Children’s Research Hospital; Estados Unido