Photophysics of fluorescent silver nanoclusters

Fluorescence imaging has been increasingly relied upon as the method of choice for many biological and medical applications. As demands for more sensitive and higher resolution imaging are ever-increasing, it is critical that photostable, and robust fluorophores capable of delivering high emission rates are available. Fluorescent silver nanoclusters offer an attractive compromise between the photostability and brightness of quantum dots and the compact versatility of organic chromophores. They have been shown to be superior in many roles, including as single molecule fluorophores and bulk multiphoton biological staining agents. The two-photon absorption cross sections are several orders of magnitude larger than commercially-available dyes, and they have demonstrated superior photostability under high intensity irradiation. In addition to the endogenous effects of the cluster, its small size of only a few atoms renders it highly susceptible to surface and environmental effects, which manifests, for example, in the observed photoinduced charge transfer between the silver cluster and oligonucleotide. This state has been shown to be highly advantageous in imaging applications, as control of this state enables better control over the time-averaged emission rate of the molecule. The mechanism of charge transfer, and the possible means by which this state can be controlled will be also be investigated in this work.Ph.D.Committee Chair: Dickson, Robert; Committee Member: Brown, Ken; Committee Member: Curtis, Jennifer; Committee Member: Payne, Christine; Committee Member: Perry, Josep

Rapid Prediction of Moments in High-rise Composite Frames Considering Cracking and Time-effects

There can be a significant amount of moment redistribution in steel concrete composite frames due to cracking, creep and shrinkage in concrete. In the present study, neural network models have been developed for rapid prediction of the inelastic moments (typically for 20 years considering cracking, creep and shrinkage in concrete) in high rise composite frames. The possibility of sagging moment being developed at ends of beams due to the substantial differential shortening of adjacent columns has also been taken into account. Closed form expressions, based on the weights and biases of the trained neural networks, are proposed to predict the inelastic moments from the elastic moments (neglecting cracking and time effects). The expressions are verified for example frames of different number of spans and storeys and errors are found to be small. The expressions require computational effort that is a fraction of that required for the available methods

Liquid-vapor and liquid-liquid interfaces of small molecule esters and ester oligomers : a molecular dynamics simulations study

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1999.Includes bibliographical references (p. 379-399).by Sandeep A. Patel.Ph.D

Chandra localization of XTE J1906+090 and discovery of its optical and infrared counterparts

We present the Chandra identification and localization of the transient X-ray source XTE J1906+090 and the discovery of its optical and infrared counterparts. Our analysis of archival Chandra ACIS-I observations of the field found the source approximately 8 away from the position determined earlier with the RXTE PCA. We have confirmed the source identification with timing analysis of the X-ray data, which detected the source spin period of 89.6 s. The best Chandra position for the source is R.A. = 19h04m47491, decl. = +09024140. Subsequently, we performed optical observations of the field around the new location and discovered a coincident optical source with R-band magnitude of 18.7. A search in the Two Micron All Sky Survey catalog revealed an infrared point source with J = 15.2, H = 14.2, and K = 13.5, whose location is also coincident with our Chandra and optical positions. Our results add fresh evidence for a Be/X-ray transient nature for XTE J1906+090

Efficacy and Safety of Atorvastatin in South Asian Patients with Dyslipidemia: An Open Label Noncomparative Pilot Study

Jeetesh V Patel1, Sandeep Gupta2, Frank Lie3, Elizabeth A Hughes11Sandwell and West Birmingham Hospitals NHS Trust, West Bromwich, UK; 2Whipps Cross and St Bartholomew’s Hospitals; and 3Whipps Cross University Hospital, London, UKBackground: Rates of coronary heart disease (CHD) mortality are 40% higher amongst South Asian men and women living in the UK compared with the general UK population. Despite an established excess CHD risk, little is known of the efficacy and safety of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) amongst South Asian migrants.Methods and results: Hyperlipidemic South Asian patients (raised or uncontrolled lowdensity lipoprotein cholesterol [LDL-C]) were recruited from two UK centers (n = 33). After a five-week period, which included dietary advice, patients received atorvastatin 10 mg/d for five weeks to achieve a target LDL-C goal of < 3.0 mmol/L, titrated to 20 mg, 40 mg, or 80 mg for a further 12 weeks as required. Significant reductions in LDL-C levels from baseline were observed after 4 weeks’ and 17 weeks’ treatment with atorvastatin (≥ 33.6%; 26.0, 41.2). Overall, 81% (95% confidence interval [CI]: 62.5, 92.6%) achieved the target LDL-C after 4 weeks’ treatment with 10 mg atorvastatin. Titration to a dose of more than 20 mg was required in only one patient (40 mg) at any point during the study. Nineteen patients reported at least one adverse event during the study; the majority were mild in severity and considered unrelated to atorvastatin.Conclusions: Atorvastatin was effective in achieving target lipid levels and was well tolerated. Statin therapy for high-risk South Asian individuals is likely to benefit CHD outcomes, although further and larger prospective trials are required.Keywords: hyperlipidemia, lipids, cholesterol, dyslipidemia, statins, coronary heart disease, South Asian

Spin-Down of the Long-Period Accreting Pulsar 4U 2206+54

4U 2206+54 is a high mass X-ray binary which has been suspected to contain a neutron star accreting from the wind of its companion BD +53 2790. Reig et al. have recently detected 5560 s period pulsations in both RXTE and INTEGRAL observations which they conclude are due to the spin of the neutron star. We present observations made with Suzaku which are contemporaneous with their RXTE observation of this source. We find strong pulsations at a period of 5554 +/- 9 s in agreement with their results. We also present a reanalysis of BeppoSAX observations of 4U 2206+54 made in 1998, in which we find strong pulsations at a period of 5420 +/- 28 seconds, revealing a spin-down trend in this long-period accreting pulsar. Analysis of these data suggests that the neutron star in this system is an accretion-powered magnetar.Comment: Submitted to The Astrophysical Journa

Development of Nano SiO2 Particles Dispersed Shape Memory Epoxy Composites

Thermo responsive shape memory epoxy based composites are being investigated for their excellent mechanical and thermal properties. In present study the thermosetting epoxy containing different composition of SiO2 nano particles ranging from 1 to 4 wt. % have been prepared through solvent casting route. Developed composites have been studied for grain analysis, FTIR, shape recovery, impact strength and hardness. Addition of 3 wt. % SiO2 improves hardness and impact strength significantly. Average grain size of SiO2 particles increase at higher wt. % of SiO2 in polymer matrix due to agglomeration of nanoparticles

Caloric Restriction Shortens Lifespan through an Increase in Lipid Peroxidation, Inflammation and Apoptosis in the G93A Mouse, an Animal Model of ALS

Caloric restriction (CR) extends lifespan through a reduction in oxidative stress, delays the onset of morbidity and prolongs lifespan. We previously reported that long-term CR hastened clinical onset, disease progression and shortened lifespan, while transiently improving motor performance in G93A mice, a model of amyotrophic lateral sclerosis (ALS) that shows increased free radical production. To investigate the long-term CR-induced pathology in G93A mice, we assessed the mitochondrial bioenergetic efficiency and oxidative capacity (CS – citrate synthase content and activity, cytochrome c oxidase - COX activity and protein content of COX subunit- I and IV and UCP3- uncoupling protein 3), oxidative damage (MDA – malondialdehyde and PC – protein carbonyls), antioxidant enzyme capacity (Mn-SOD, Cu/Zn-SOD and catalase), inflammation (TNF-α), stress response (Hsp70) and markers of apoptosis (Bax, Bcl-2, caspase 9, cleaved caspase 9) in their skeletal muscle. At age 40 days, G93A mice were divided into two groups: Ad libitum (AL; n = 14; 7 females) or CR (n = 13; 6 females), with a diet equal to 60% of AL. COX/CS enzyme activity was lower in CR vs. AL male quadriceps (35%), despite a 2.3-fold higher COX-IV/CS protein content. UCP3 was higher in CR vs. AL females only. MnSOD and Cu/Zn-SOD were higher in CR vs. AL mice and CR vs. AL females. MDA was higher (83%) in CR vs. AL red gastrocnemius. Conversely, PC was lower in CR vs. AL red (62%) and white (30%) gastrocnemius. TNF-α was higher (52%) in CR vs. AL mice and Hsp70 was lower (62%) in CR vs. AL quadriceps. Bax was higher in CR vs. AL mice (41%) and CR vs. AL females (52%). Catalase, Bcl-2 and caspases did not differ. We conclude that CR increases lipid peroxidation, inflammation and apoptosis, while decreasing mitochondrial bioenergetic efficiency, protein oxidation and stress response in G93A mice

Jet Breaks in Short Gamma-Ray Bursts. I: The Uncollimated Afterglow of GRB 050724

We report the results of the \chandra observations of the \swift-discovered short Gamma-Ray Burst GRB 050724. \chandra observed this burst twice, about two days after the burst and a second time three weeks later. The first \chandra pointing occurred at the end of a strong late-time flare. About 150 photons were detected during this 49.3 ks observation in the 0.4-10.0 keV range. The spectral fit is in good agreement with spectral analysis of earlier \swift XRT data. In the second \chandra pointing the afterglow was clearly detected with 8 background-subtracted photons in 44.6 ks. From the combined \swift XRT and \chandra-ACIS-S light curve we find significant flaring superposed on an underlying power-law decay slope of $\alpha$=0.98$^{+0.11}_{-0.09}$. There is no evidence for a break between about 1 ks after the burst and the last \chandra pointing about three weeks after the burst. The non-detection of a jet break places a lower limit of 25$^{\circ}$ on the jet opening angle, indicating that the outflow is less strongly collimated than most previously-reported long GRBs. This implies that the beaming corrected energy of GRB 050724 is at least $4\times 10^{49}$ ergs.Comment: 7 pages, ApJ acceped, scheduled for December 20, 2006, ApJ, 65

A possible magnetar nature for IGR J16358-4726

We present detailed spectral and timing analysis of the hard X-ray transient IGR J16358-4726 using multisatellite archival observations. A study of the source flux time history over 6 yr suggests that lower luminosity transient outbursts can be occurring in intervals of at most 1 yr. Joint spectral fits of the higher luminosity outburst using simultaneous Chandra ACIS and INTEGRAL ISGRI data reveal a spectrum well described by an absorbed power-law model with a high-energy cutoff plus an Fe line. We detected the 1.6 hr pulsations initially reported using Chandra ACIS also in the INTEGRAL ISGRI light curve and in subsequent XMM-Newton observations. Using the INTEGRAL data, we identified a spin-up of 94 s ( = 1.6 × 10-4), which strongly points to a neutron star nature for IGR J16358-4726. Assuming that the spin-up is due to disk accretion, we estimate that the source magnetic field ranges between 1013 and 1015 G, depending on its distance, possibly supporting a magnetar nature for IGR J16358-4726