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Biomedical subjects

V Prasad

Publications and source records attributed to V Prasad.

At least 19 recordsLinked to original sources
PubMed2006

A genetic toolbox for creating reversible Ca2+-sensitive materials.

A major goal of polymer science is to develop "smart" materials that sense specific chemical signals in complex environments and respond with predictable changes in their mechanical properties. Here, we describe a genetic toolbox of natural and engineered protein modules that can be rationally combined in manifold ways to create reversible self-assembling materials that vary in their composition, architecture, and mechanical properties. Using this toolbox, we produced several materials that reversibly self-assemble in the presence of Ca2+ and characterized these materials using particle-tracking microrheology. The properties of these materials could be predicted from the dilute solution behavior of their component modules, suggesting that this toolbox may be generally useful for creating new stimuli-sensitive materials.

Calcium↗
PubMed2006

Two-particle microrheology of quasi-2D viscous systems.

We study the spatially correlated motions of colloidal particles in a quasi-2D system (human serum albumin protein molecules at an air-water interface) for different surface viscosities eta s. We observe a transition in the behavior of the correlated motion, from 2D interface dominated at high eta s to bulk fluid dependent at low eta s. The correlated motions can be scaled onto a master curve which captures the features of this transition. This master curve also characterizes the spatial dependence of the flow field of a viscous interface in response to a force. The scale factors used for the master curve allow for the calculation of the surface viscosity eta s that can be compared to one-particle measurements.

2-Propanol↗
PubMed2006

Microscopic structure and elasticity of weakly aggregated colloidal gels.

We directly probe the microscopic structure, connectivity, and elasticity of colloidal gels using confocal microscopy. We show that the gel is a random network of one-dimensional chains of particles. By measuring thermal fluctuations, we determine the effective spring constant between pairs of particles as a function of separation; this is in agreement with the theory for fractal chains. Long-range attractions between particles lead to freely rotating bonds, and the gel is stabilized by multiple connections among the chains. By contrast, short-range attractions lead to bonds that resist bending, with dramatically suppressed formation of loops of particles.

Journal Article↗
PubMed2006

Multidimensional assessment of female tracheoesophageal prosthetic speech.

OBJECTIVE: The objective of this study was to undertake a multidimensional assessment of female tracheoesophageal prosthetic speech. STUDY DESIGN: A cross-sectional cohort study. SETTING: Head and Neck Unit in a tertiary oncology referral centre. PATIENTS: Ten female and 10 male total laryngectomy patients with no signs of recurrence and using voice prosthesis were compared to 10 normal female speakers. INTERVENTION(S): Electroglottographic and acoustic analysis of voice parameters for both sustained vowel /i/ and connected speech, perceptual evaluation using GRBAS (with 2 experienced raters) and questionnaire assessment using the University of Washington Quality of Life and the Voice Handicap Index. Statistical analysis was done using the Statistical Package for Social Sciences, (v. 14, SPSS Inc., Chicago III). RESULTS: Median age of the female larygectomy patients was 65 years (range: 41-81), that of male laryngectomees was 66.5 years (range: 40-79) and that of the normal female subjects was 47.5 years (range: 35-72). All electroglottographic, acoustic parameters and GRBAS ratings of the female laryngectomy patients were significantly worse as compared with the normal female subjects. The median fundamental frequency (111.8 Hz) was comparable to male tracheoesophageal speakers (115.8 Hz). Mean composite University of Washington Quality of Life score and overall Voice Handicap Index score was 79.3(12.5) and 47.5(27.6) for the female laryngectomy patients and for the males was 81.2 (9.6) and 39.4(18.7). CONCLUSIONS: Gender frequency differences as seen in normal subjects are lost following a laryngectomy operation as evidenced by electroglottographic and perceptual data. Although the quality of life scores are comparable to the male tracheoesophageal speakers, they exhibit a greater voice handicap as compared to their male counterparts.

Adult↗
PubMed2006

Questionnaire analysis of the swallowing-related outcomes following total laryngectomy.

OBJECTIVE: To determine the effects of a total laryngectomy on the swallow and subsequent quality of life in head and neck cancer patients. DESIGN: Cross-sectional single centre cohort study. SETTING: Head and Neck Oncology Unit, Tertiary Referral Unit. PATIENTS: Sixty-two patients who underwent total laryngectomy at our centre participated in the study. METHODS: Subjects were stratified by age, sex, tumour stage, other procedures such as myotomy and nerve re-implantation. Pharyngectomy, glossectomy, flap reconstruction, neck dissection and previous radio- and chemotherapy were also assessed to see if they affected swallow and subsequent quality of life. Main outcome was measured using the MD Anderson Dysphagia Inventory questionnaire. RESULTS: Responses were received from 46 males and 16 females (response rate of 80.5%) with a mean age of 64.7 years (SD 9.4). Median follow-up in patients was 90 months (range 1-276). The mean MD Anderson Dysphagia Inventory total score in our series of patients was 77.7 (SD 16.6). MD Anderson Dysphagia Inventory global score was 79.4 (SD 22.6), Emotional score was 77.7 (SD 17.8), Functional score 81.3 (SD 15.9) and Physical score was 74.1(SD 18). Statistically significant differences were seen between the emotional scores of glossectomised and non-glossectomised patients (Mann Whitney, P = 0.04). No significant correlation was seen between the subscale scores and the remaining treatment variables such as age, gender, site, tumour stage, myotomy, nerve implantation, radiotherapy, reconstruction and major complications. CONCLUSION: This questionnaire study is the largest of its type to assess the swallow of patients who have undergone laryngectomy at a single centre. The overall result confirmed that most patients had a subjectively good swallow. Only glossectomy and the method of PE segment closure were shown to significantly affect swallowing outcomes following surgery. We recommend further work especially prospective studies pre and post surgery using this or similarly validated instruments to fully assess swallow in the laryngectomy population.

Adult↗
PubMed2005

Observation of the decay xi0 --> sigma+ mu- nu(mu).

The xi0 muon semileptonic decay has been observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the xi0 beta decay mode and yields a value for the ratio of decay rates gamma(xi0 --> sigma+ mu- nu(mu))/gamma(xi0 --> sigma+ e- nu(e)) of [1.8(-0.5)(+0.7)(stat) +/- 0.2(syst)] x 10(-2). This is in agreement with the SU(3) flavor symmetric quark model.

Journal Article↗
PubMed2005

Inside-out disruption of silica/gold core-shell nanoparticles by pulsed laser irradiation.

Near-infrared (NIR) femtosecond laser irradiation of metallodielectric core-shell silica-gold (SiO(2)-Au) nanoparticles can induce extreme local heating prior to the rapid dissipation of energy caused by the large surface area/volume ratio of nanometer-scale objects. At low pulse intensities, the dielectric silica core is removed, leaving an incomplete gold shell behind. The gold shells with water inside and out still efficiently absorb NIR light from subsequent pulses, showing that a complete shell is not necessary for absorption. At higher pulse intensities, the gold shell itself is melted and disrupted, leading to smaller, approximately 20-nm gold nanoparticles. Spectroscopic measurements show that this disruption is accompanied by optical hole burning of the peak at 730 nm and formation of a new peak at 530 nm. The silica removal and gold shell disruption confirms significant temperature rise of the core-shall nanoparticle. However, the entire process leads to minimal heating of the bulk solution due to the low net energy input.

Gold↗
PubMed2005

Time-dependent strength of colloidal gels.

Colloidal silica gels are shown to stiffen with time, as demonstrated by both dynamic light scattering and bulk rheological measurements. Their elastic moduli increase as a power law with time, independent of particle volume fraction; however, static light scattering indicates that there are no large-scale structural changes. We propose that increases in local elasticity arising from bonding between neighboring colloidal particles can account for the strengthening of the network, while preserving network structure.

Journal Article↗
PubMed2005

Light-induced changes of optical and electrical properties in bent-core azo compounds.

We have studied the optical and electrical properties of two bent-core substances with an azo linkage in their cores. Pump-probe laser studies, direct textural observations, and spectrophotometric recordings show an initial decrease of light transmission, which at larger light intensities (approximately 1 mW/mm2) is followed by a bleaching. Simultaneously the electrical properties (electric conductivity, antiferroelectric polarization, switching threshold, and switching time) decreased monotonically with increasing light intensities. The monotonic decrease of electrical properties indicates that the darkening and bleaching have the same origin, namely, the photochemical isomerization of the azo linkage from the trans to the cis isomer. The material with cis isomer has a lower clearing point and phase separates from the trans-rich domains. Initially the size of the separated isotropic domains is below the visible range, which causes increased scattering. As the size of the isotropic domains increase the scattering disappears and the transmittance becomes the average of the transmittances in the polar tilted smectic and isotropic phases.

Journal Article↗
PubMed2004

A determination of the Cabibbo-Kobayashi-Maskawa parameter |V us| using KL decays.

We present a determination of the Cabibbo-Kobayashi-Maskawa parameter |V(us)| based on new measurements of the six largest K(L) branching fractions and semileptonic form factors by the KTeV (E832) experiment at Fermilab. We find |V(us)|=0.2252+/-0.0008(KTeV)+/-0.0021(ext), where the errors are from KTeV measurements and from external sources. We also use the measured branching fractions to determine the CP violation parameter |eta(+-)|=(2.228+/-0.005(KTeV)+/-0.009(ext))x10(-3).

Journal Article↗
PubMed2004

Limits to gelation in colloidal aggregation.

We show that the dynamics of large fractal colloid aggregates are well described by a combination of translational and rotational diffusion and internal elastic fluctuations, allowing both the aggregate size and internal elasticity to be determined by dynamic light scattering. The comparison of results obtained in microgravity and on Earth demonstrates that cluster growth is limited by gravity-induced restructuring. In the absence of gravity, thermal fluctuations ultimately inhibit fractal growth and set the fundamental limitation to the lowest volume fraction which will gel.

Colloids↗
PubMed2004

Search for the rare decay K(L)-->pi(0)e(+)e(-).

The KTeV/E799 experiment at Fermilab has searched for the rare kaon decay K(L)-->pi(0)e(+)e(-). This mode is expected to have a significant CP violating component. The measurement of its branching ratio could support the standard model or could indicate the existence of new physics. This Letter reports new results from the 1999-2000 data set. One event is observed with an expected background at 0.99+/-0.35 events. We set a limit on the branching ratio of 3.5x10(-10) at the 90% confidence level. Combining with the previous result based on the data set taken in 1997 yields the final KTeV result: BR(K(L)-->pi(0)e(+)e(-))<2.8x10(-10) at 90% C.L.

Journal Article↗
PubMed2003

Measurements of the Decay KL-->e+ e- mu+ mu-.

The KTeV experiment at Fermilab has isolated a total of 132 events from the rare decay K(L)-->e+ e- mu+ mu-, with an estimated background of 0.8 events. The branching ratio of this mode is determined to be [2.69+/-0.24(stat)+/-0.12(syst)]x10(-9), with a radiative cutoff of M(2)(ee mu mu)/M(2)(K)>0.95. The first measurement using this mode of the parameter alpha from the D'Ambrosio-Isidori-Portolès (DIP) model of the K(L)gamma*gamma* vertex yields a result of -1.59+/-0.37, consistent with values obtained from other decay modes. Because of the limited statistics, no sensitivity is found to the DIP parameter beta. We use this decay mode to set limits on CP and lepton violation.

Journal Article↗
PubMed2003

Agrobacterium tumefaciens-mediated transformation of an Oncidium orchid.

The present protocol was aimed at establishing a routine transformation procedure via Agrobacterium tumefaciens for an important Oncidium orchid cultivar. An expression vector containing hptII and gusA genes driven by the cauliflower mosaic virus (CaMV) 35S promoter was successfully introduced into the Oncidium orchid genome by A. tumefaciens. Protocorm-like bodies (PLBs) derived from protocorms, were the target explants for transformation. The transformation was performed through two stages of cocultivation, the first stage occurring on antibiotic-free medium for 3 days, and the subsequent stage on medium containing 100 mg/l timentin for 1 month. Among 1,000 inoculated PLBs, 108 putatively transformed PLBs were proliferated on 5 mg/l hygromycin selection medium. A total of 28 independent transgenic orchid plants were obtained, from which six transgenic lines that were positive for beta-glucuronidase were randomly selected and confirmed by Southern, northern and western blot analyses. These results indicated that the foreign DNA was successfully integrated into the orchid genome and expressed transcriptionally and translationally in these orchid plants. The present transformation method reported is suitable for improving the Oncidium orchid through genetic engineering.

Agrobacterium tumefaciens↗
PubMed2003

Rideal lecture. Universal features of the fluid to solid transition for attractive colloidal particles.

Attractive colloidal particles can exhibit a fluid to solid phase transition if the magnitude of the attractive interaction is sufficiently large, if the volume fraction is sufficiently high, and if the applied stress is sufficiently small. The nature of this fluid to solid transition is similar for many different colloid systems, and for many different forms of interaction. The jamming phase transition captures the common features of these fluid to solid translations, by unifying the behavior as a function of the particle volume fraction, the energy of interparticle attractions, and the applied stress. This paper describes the applicability of the jamming state diagram, and highlights those regions where the fluid to solid transition is still poorly understood. It also presents new data for gelation of colloidal particles with an attractive depletion interaction, providing more insight into the origin of the fluid to solid transition.

Journal Article↗
PubMed2003

Remuneration for blood donation and attitudes towards blood donation and receipt in Leeds.

In a survey of attitudes towards remuneration for blood donation in Leeds, the following questions were completed by 489 adults (N), of whom 89 were regular donors, 105 were lapsed donors and 295 had never donated: 'If you needed blood, would you be content if the donor had been paid: yes/no'. 'If I were paid enough I would be less/equally/more likely to donate blood '. The majority (67.7%) of potential recipients would be content if the donor had been paid. The prospect of remuneration made 16.4% of respondents more likely and 14.5% less likely to donate. As the difference is less than 2% of N, offering remuneration may not lead to a significant increase in the number of donations. A statistical comparison (chi2 = 45, d.f. = 2, P << 0.001) showed associations between the responses 'more likely to donate if paid' and 'content to receive blood from a paid donor', and between the responses 'less likely to donate if paid' and 'not content to receive blood from a paid donor'. Age distributions are presented for the donor status categories and the responses to the main questions. Of 129 people who stated a minimum, nonzero payment that would persuade them to donate, 103 (80%) suggested pound sterling 10 or less.

Adolescent↗
PubMed2003

Effects of point mutations in the major capsid protein of beet western yellows virus on capsid formation, virus accumulation, and aphid transmission.

Point mutations were introduced into the major capsid protein (P3) of cloned infectious cDNA of the polerovirus beet western yellows virus (BWYV) by manipulation of cloned infectious cDNA. Seven mutations targeted sites on the S domain predicted to lie on the capsid surface. An eighth mutation eliminated two arginine residues in the R domain, which is thought to extend into the capsid interior. The effects of the mutations on virus capsid formation, virus accumulation in protoplasts and plants, and aphid transmission were tested. All of the mutants replicated in protoplasts. The S-domain mutant W166R failed to protect viral RNA from RNase attack, suggesting that this particular mutation interfered with stable capsid formation. The R-domain mutant R7A/R8A protected approximately 90% of the viral RNA strand from RNase, suggesting that lower positive-charge density in the mutant capsid interior interfered with stable packaging of the complete strand into virions. Neither of these mutants systemically infected plants. The six remaining mutants properly packaged viral RNA and could invade Nicotiana clevelandii systemically following agroinfection. Mutant Q121E/N122D was poorly transmitted by aphids, implicating one or both targeted residues in virus-vector interactions. Successful transmission of mutant D172N was accompanied either by reversion to the wild type or by appearance of a second-site mutation, N137D. This finding indicates that D172 is also important for transmission but that the D172N transmission defect can be compensated for by a "reverse" substitution at another site. The results have been used to evaluate possible structural models for the BWYV capsid.

Amino Acid Sequence↗