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G C Schatz

Publications and source records attributed to G C Schatz.

15 recordsLinked to original sources
PubMed2005

Theory and method for calculating resonance Raman scattering from resonance polarizability derivatives.

We present a method to calculate both normal Raman-scattering (NRS) and resonance Raman-scattering (RRS) spectra from the geometrical derivatives of the frequency-dependent polarizability. In the RRS case, the polarizability derivatives are calculated from resonance polarizabilities by including a finite lifetime of the electronic excited states using time-dependent density-functional theory. The method is a short-time approximation to the Kramers, Heisenberg, and Dirac formalism. It is similar to the simple excited-state gradient approximation method if only one electronic excited state is important, however, it is not restricted to only one electronic excited state. Since the method can be applied to both NRS and RRS, it can be used to obtain complete Raman excitation profiles. To test the method we present the results for the S2 state of uracil and the S4, S3, and S2 states of pyrene. As expected, the results are almost identical to the results obtained from the excited-state gradient approximation method. Comparing with the experimental results, we find in general quite good agreement which enables an assignment of the experimental bands to bands in the calculated spectrum. For uracil the inclusion of explicit waters in the calculations was found to be necessary to match the solution spectra. The calculated resonance enhancements are on the order of 10(4)-10(6), which is in agreement with experimental findings. For pyrene the method is also able to distinguish between the three different electronic states for which experimental data are available. The neglect of anharmonicity and solvent effects in the calculations leads to some discrepancy between theory and experiment.

Journal Article↗
PubMed2005

Finite lifetime effects on the polarizability within time-dependent density-functional theory.

We present an implementation for considering finite lifetime of the electronic excited states into linear-response theory within time-dependent density-functional theory. The lifetime of the excited states is introduced by a common phenomenological damping factor. The real and imaginary frequency-dependent polarizabilities can thus be calculated over a broad range of frequencies. This allows for the study of linear-response properties both in the resonance and nonresonance cases. The method is complementary to the standard approach of calculating the excitation energies from the poles of the polarizability. The real and imaginary polarizabilities can then be calculated in any specific energy range of interest, in contrast to the excitation energies which are usually solved only for the lowest electronic states. We have verified the method by investigating the photoabsorption properties of small alkali clusters. For these systems, we have calculated the real and imaginary polarizabilities in the energy range of 1-4 eV and compared these with excitation energy calculations. The results showed good agreement with both previous theoretical and experimental results.

Journal Article↗
PubMed2004

Quantum and classical studies of the O(3P) + H2(v = 0-3,j = 0) --> OH + H reaction using benchmark potential surfaces.

We present results of time-dependent quantum mechanics (TDQM) and quasiclassical trajectory (QCT) studies of the excitation function for O(3P) + H2(v = 0-3,j = 0) --> OH + H from threshold to 30 kcal/mol collision energy using benchmark potential energy surfaces [Rogers et al., J. Phys. Chem. A 104, 2308 (2000)]. For H2(v = 0) there is excellent agreement between quantum and classical results. The TDQM results show that the reactive threshold drops from 10 kcal/mol for v = 0 to 6 for v = 1, 5 for v = 2 and 4 for v = 3, suggesting a much slower increase in rate constant with vibrational excitation above v = 1 than below. For H2(v > 0), the classical results are larger than the quantum results by a factor approximately 2 near threshold, but the agreement monotonically improves until they are within approximately 10% near 30 kcal/mol collision energy. We believe these differences arise from stronger vibrational adiabaticity in the quantum dynamics, an effect examined before for this system at lower energies. We have also computed QCT OH(v',j') state-resolved cross sections and angular distributions. The QCT state-resolved OH(v') cross sections peak at the same vibrational quantum number as the H2 reagent. The OH rotational distributions are also quite hot and tend to cluster around high rotational quantum numbers. However, the dynamics seem to dictate a cutoff in the energy going into OH rotation indicating an angular momentum constraint. The state-resolved OH distributions were fit to probability functions based on conventional information theory extended to include an energy gap law for product vibrations.

Journal Article↗
PubMed2003

Anomalous surface diffusion in nanoscale direct deposition processes.

We report the first observation of anomalous diffusion in nanometer scale direct deposition processes utilizing dip-pen nanolithography (DPN). DPN permits quite general nanostructure patterns to be drawn on flat surfaces. Here we demonstrate experimentally, and discuss theoretically, the situation in which the molecular ink in DPN binds weakly to the surface. We observe, for the weak-binding case of 1-dodecylamine on mica, that anomalous diffusion occurs, leading to nearly fractal deposition patterns.

Journal Article↗
PubMed2001

Photoinduced conversion of silver nanospheres to nanoprisms.

A photoinduced method for converting large quantities of silver nanospheres into triangular nanoprisms is reported. The photo-process has been characterized by time-dependent ultraviolet-visible spectroscopy and transmission electron microscopy, allowing for the observation of several key intermediates in and characteristics of the conversion process. This light-driven process results in a colloid with distinctive optical properties that directly relate to the nanoprism shape of the particles. Theoretical calculations coupled with experimental observations allow for the assignment of the nanoprism plasmon bands and for the first identification of two distinct quadrupole plasmon resonances for a nanoparticle. Unlike the spherical particles they are derived from that Rayleigh light-scatter in the blue, these nanoprisms exhibit scattering in the red, which could be useful in developing multicolor diagnostic labels on the basis not only of nanoparticle composition and size but also of shape.

Anisotropy↗
PubMed2000

Infant and adolescent hepatitis B immunization up to 1999: a global overview.

This article presents a global overview of hepatitis B infant and adolescent immunization programmes. The 108 reported universal infant or adolescent immunization programmes and 87 reported national infant coverage rates fit a pattern, explained by hepatitis B endemicity, prosperity, policy emphasis, and immunization programme strength. Most East and Southeast Asian, Pacific, and Middle Eastern countries have intermediate to highly endemic hepatitis B. Most have achieved 65-100% coverage. South and Central Asia and sub-Saharan Africa have intermediate to high endemicity, with some countries having hepatitis B immunization programmes. Some Southern and Eastern European countries, with intermediate endemicity, have high coverage. Low endemic Northern European countries vaccinate higher risk groups; some have universal infant or adolescent programmes. Caribbean and Latin American countries have varying endemicity, and most started programmes. Low endemic North American countries have universal vaccination programmes. Universal immunization strategies have greatly reduced incidence and prevalence, and are cost-effective for many countries, but many have difficulties affording this vaccine. Globally, most infants are not being immunized against hepatitis B virus infection. Increasing coverage, and decreasing the numbers of people diseased and dying from this virus, may require delivering heat-stable vaccine beyond cold chains, creative financing to reduce prices, and multivalent vaccines.

Adolescent↗
PubMed1993

Effect of a hepatitis B vaccination program on the prevalence of hepatitis B virus infection.

In April 1991, surveys for serologic evidence of hepatitis B virus (HBV) infection were conducted among 3- to 4-year-old children born after a hepatitis B immunization program of newborns began and among 6- to 11-year-old children targeted for early childhood vaccination in American Samoa. Compared with 3- to 4-year-olds tested in 1991, children tested at baseline in 1985 were more likely to have been infected with HBV (5/40 vs. 2/93; prevalence ratio [PR] = 5.8, 95% confidence limits [CL] = 1.2, 28.7) and to have chronic infection with HBV (3/40 vs. 0/95; PR = undefined, lower CL = 1.2). Compared with 6- to 11-year-olds tested in 1991, children in 1985 were more likely to have been infected with HBV (32/121 vs. 53/386; PR = 1.9, CL = 1.3, 2.8) and to have chronic infection with HBV (8/121 vs. 7/386; PR = 3.6, CL = 1.3, 9.8). The incorporation of hepatitis B vaccine into routine childhood vaccination schedules can prevent acute and chronic HBV infection in areas of high endemicity.

Child↗
PubMed1993

Hepatitis B virus infection in Honolulu students.

OBJECTIVES: To determine hepatitis B virus (HBV) carrier and infection rates and HBV epidemiology in Honolulu students. DESIGN: Cross-sectional survey. SETTING: Honolulu public elementary, intermediate, and high schools. PATIENTS: A volunteer sample of 4936 students from 43 Honolulu schools. MAIN OUTCOME MEASURES: HBV carrier rate (presence of hepatitis B surface antigen) and infection rate (presence of either hepatitis B surface antigen, antibody to hepatitis B surface antigen, antibody to hepatitis B core antigen, or any combinations of these) by school grade, ethnicity, and place of birth. RESULTS: Eighty-three (1.68%) students were identified as HBV carriers, and a total of 353 (7.15%) students had serologic evidence of infection. Infection rates increased from elementary school age to high school age, more so in Asian/Pacific Island-born students. The prevalence of infection was higher in Asian/Pacific Island-born students than in those born in the United States. The majority of infected Hawaiian-born students were first-generation Asian/Pacific Island Americans. CONCLUSIONS: Horizontal transmission of HBV occurs in Honolulu school-age children. HBV immunization of all infants in Hawaii, not just those born to carrier mothers, is necessary to reduce HBV transmission in Hawaii.

Adolescent↗
PubMed1990

Development of recommendations for control of hepatitis B virus infections: the role of cost analysis.

Hepatitis B (HBV) infection produces a number of acute and chronic consequences including fulminant hepatitis, chronic liver disease and cirrhosis. The development of safe and effective hepatitis B vaccines has led to the development of several prevention strategies based on the endemicity and primary age of infection in the population. In areas of high endemicity of infection, universal immunization of infants has been advocated and appears feasible. However, in areas of low endemicity of infection, selected high risk group immunization of adults has been recommended but has not been successful in changing infection rates. In 1981, an analysis of the economic consequences of acute and chronic HBV-related liver disease showed an expenditure of at least US$197 million for direct medical costs and US$126 million for the associated cost of work-loss. These results suggest the more widespread use of hepatitis B vaccine to prevent these high health-related costs.

Chronic Disease↗
PubMed1988

Postmarketing surveillance for neurologic adverse events reported after hepatitis B vaccination. Experience of the first three years.

In 1982, the Centers for Disease Control, the Food and Drug Administration, and the manufacturer created a surveillance system to monitor spontaneous reports of adverse events occurring after inoculation with the new plasma-derived hepatitis B vaccine (Heptavax-B, Merck Sharp and Dohme, West Point, PA). In the three years between June 1, 1982 and May 31, 1985, an estimated 850,000 persons received the vaccine. During that period, a total of 41 reports were received for one of the following neurologic adverse events: convulsions (five cases), Bell's palsy (10 cases), Guillain-Barré syndrome (nine cases), lumbar radiculopathy (five cases), brachial plexus neuropathy (three cases), optic neuritis (five cases), and transverse myelitis (four cases). Half of these occurred after the first of three required vaccine doses. There were no deaths. Calculation of the relative risks of these illnesses after hepatitis B vaccination was highly dependent on diagnostic classification of the cases, estimates of the size of the vaccinated population, background incidence of the diseases, and the length and distribution of the hypothetical at-risk interval used in the analysis. Other factors important in judging the results of the study could not be measured, including underreporting. In some analyses, Guillain-Barré syndrome was reported significantly more often than expected (p less than 0.05, Poisson probability distribution). However, no conclusive epidemiologic association could be made between any neurologic adverse event and the vaccine. Even if such an association did exist, the preventive benefits of the vaccine in persons at high risk for hepatitis B would unequivocally outweigh the risk of any neurologic adverse event.

Evaluation Studies as Topic↗
PubMed1987

A hepatitis B vaccination program in a community teaching hospital.

Prior to offering the hepatitis B (HB) vaccine, a prescreen for hepatitis B virus (HBV) antibodies was conducted in a 565 bed hospital in Pasadena, California. Antibodies to the hepatitis B virus were detected in 14.5% of 1,745 employees tested. There was a significantly higher prevalence in those with a previous history of hepatitis, blood transfusions, exposure to needlesticks, number of years in the same occupation, and in the same hospital work area. Employees of Asian extraction (33.3%) and blacks (23.1%) had a higher prevalence of antibodies to the hepatitis B virus than Hispanics (13.7%) and whites (10.2%). Anti-HBs was detected in 92.6% of 865 employees who received three doses of the hepatitis B vaccine. Only 28.6% of nonresponders receiving a fourth dose of hepatitis B vaccine produced anti-HBs. The nonresponders to the HB vaccine were older (average age 64.9 years) when compared to the responders (average age 37.5 years), and more males failed to produce anti-HBs after vaccination than females. Hepatitis B vaccination of the majority of individuals with either "low level" anti-HBs alone or anti-HBc alone did not elicit an anamnestic response after one dose of vaccine, implying that these "low level" antibodies are nonspecific and do not represent antiviral antibodies. Adverse reactions to the hepatitis B vaccine were minor and included a flu-like syndrome, sore arm, and rash and swelling at the injection site. The reasons for nonparticipation were obtained from 179 individuals, and the main issue was concern about safety of the hepatitis B vaccine.

Adult↗
PubMed1985

A multicenter study of the epidemiology of hepatitis B in anesthesia residents.

Practicing anesthesiologists are at high risk of hepatitis B infection, but the risk for anesthesia residents has not been assessed. Anesthesia residents at seven universities were surveyed to study the epidemiology of hepatitis B in these trainees. Hepatitis B virus markers in serum were measured and data from questionnaires were used to determine characteristics of anesthetic practice, effectiveness of strategies for hepatitis B virus infection control, and nonvocational hepatitis B risk factors. Of 267 participants, 12.7% (range of the seven centers, 8.7%-22.7%) had serum markers for hepatitis B virus. The seropositivity (17.8%) in anesthesia residents who had completed more than 12 months of nonanesthesia postgraduate clinical training, or who had practiced medicine in another specialty prior to anesthesia, was greater than in the other trainees (9.4%). Based on their risk and the ineffectiveness of current control measures, anesthesia residents who lack hepatitis B virus immunity should be vaccinated prior to or as early as possible in their training.

Anesthesiology↗
PubMed1984

A multicenter study of the prevalence of hepatitis B viral serologic markers in anesthesia personnel.

Health care workers with frequent blood contact are at high risk of infection with hepatitis B virus. We surveyed 154 physician anesthesiologists (MD) and certified registered nurse anesthetists (CRNA) at four university-affiliated medical centers to determine the prevalence of serologic markers of hepatitis B virus (HBV). Questionnaires were used to ascertain historical and demographic information, nonoccupational risk factors, and characteristics of the participants' anesthesia practice. The overall prevalence of seropositivity was 18.8% (range 10.2-30.3%), and there were no statistically significant differences among the four centers, MD and CRNA groups, or males and females. In contrast to other studies, the prevalence of seropositive markers did not increase with an increase in the participants' age or length of time in the specialty. For the groups sampled in this study, geographic location or type of practice did not influence the increased prevalence of HBV seropositivity in anesthesia personnel. The current methods of HBV infection control were not associated with a decreased prevalence of serum markers. The majority of the susceptible anesthesia personnel at these four institutions did not plan to receive the hepatitis B vaccine when surveyed at the time of this study.

Anesthesiology↗
PubMedDate not supplied

Availability and use of hepatitis B vaccine in laboratory and nursing schools in the United States.

Hepatitis B is a well-documented occupational hazard for health care workers, including both laboratory and nursing personnel. Since the development of effective hepatitis B vaccines, the Immunization Practices Advisory Committee (ACIP) has recommended that health care workers receive the vaccine. In this study, 78 laboratory training programs and 83 nursing training programs were surveyed regarding availability and usage of hepatitis B vaccine. The hepatitis B vaccine was made available to students in 81 percent of the laboratory programs and 23 percent of the nursing programs. In those programs making the vaccine available, only 59 percent of the laboratory programs and 5 percent of the nursing programs reported a high (greater than 75 percent) use by students. Concern about cost and payment for the vaccine was the most common reason (80 percent) noted by laboratory schools that did not have hepatitis B vaccination programs for students. Of the nursing schools that did not have vaccine programs, 58 percent had not yet considered a program. At laboratory schools with vaccination programs, who paid for the vaccine (hospital or school versus student) was among the most important determinants for vaccine usage by students. These findings point out that some laboratory schools and many nursing schools have not applied the ACIP recommendations to their own programs. Educational efforts and creative payment plans for the vaccine are needed to increase the availability and use of hepatitis B vaccine among laboratory and nursing students.

Hepatitis B↗