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Biomedical subjects

S A Alexander

Publications and source records attributed to S A Alexander.

At least 19 recordsLinked to original sources
PubMed2006

Oscillator strengths of helium computed using Monte Carlo methods.

We have optimized trial wave functions for the three lowest states of the helium atom with symmetry 1S, 1P, 1D, 3S, 3P, and 3D using variational Monte Carlo methods. With these wave functions we then computed dipole oscillator strengths for the 1S-1P, 1P-1D, 3S-3P, and 3P-3D transitions using the length, velocity, and acceleration forms. Our values are in good agreement with the best results found in the literature.

Journal Article↗
PubMed2004

A ground state potential energy surface for H2 using Monte Carlo methods.

Using variational Monte Carlo and a simple explicitly correlated wave function we have computed the Born-Oppenheimer energy of the H2 ground state (X 1Sigmag+) at 24 internuclear distances. We have also calculated the diagonal correction to the Born-Oppenheimer approximation and the lowest-order relativistic corrections at each distance using variational Monte Carlo techniques. The nonadiabatic values are evaluated from numerical derivatives of the wave function with respect to the nuclear coordinates. With this potential energy surface we have computed several of the lowest vibrational-rotational energies for this system. Our results are in good agreement with the best values found in the literature.

Journal Article↗
PubMed2004

Properties of selected diatomics using variational Monte Carlo methods.

Using variational Monte Carlo and highly accurate trial wave functions optimized by Filippi and Umrigar, we calculate a number of molecular properties for the ground state of Li2, Be2, B2, C2, N2, O2, and F2. This is the first time that many of these properties have been computed.

Journal Article↗
PubMed2000

Effects of self-applied topical fluoride preparations in orthodontic patients.

The purpose of this study was to compare the effectiveness of toothbrushing followed by fluoride rinsing, fluoride gel brushing, or fluoride gel dentifrice brushing alone in controlling the demineralization that often follows orthodontic treatment. Seventy-eight consecutive adolescent patients undergoing orthodontic care were divided into 3 groups: group 1 (control) used a low-potency, high-frequency fluoride rinse; group 2 used a high-potency, high-frequency fluoride brush-on gel; and group 3 used a high-potency, high-frequency fluoride gel dentifrice. When pretreatment levels of demineralization were subtracted from posttreatment values, both gel groups displayed a significant difference (P < .05) in smooth surface demineralization sites when compared to controls. Reversal of white-spot lesions occurred in 15% of sites that exhibited pathology as a result of the fluoride and preventive regimen. These results indicate that a daily use of a 5000-ppm fluoride gel along with toothbrushing with a fluoride paste or brushing twice daily with a 5000-ppm fluoride dentifrice alone provides greater protection beyond that of tooth-brushing with a fluoride paste (1000 ppm) and rinsing with a 0.05% sodium fluoride rinse.

Adolescent↗
PubMed1999

Relativistic calculations using Monte Carlo methods: one-electron systems.

Variance minimization and Monte Carlo integration are used to evaluate the four-component Dirac equation for a number of one-electron atomic and diatomic systems. This combination produces accurate energies, is relatively simple to implement, and exhibits few of the problems associated with traditional techniques.

Journal Article↗
PubMed1997

Overview of anterior and posterior crossbites in children.

Crossbites are a prevalent condition in children. They represent a challenge to the clinician in both diagnosis and treatment planning. Crossbites may be dental or skeletal in etiology. A thorough clinical assessment and accurate records are necessary. Treatment modalities will vary according to the specific diagnosis.

Child↗
PubMed1996

Bond strength of rebonded orthodontic brackets.

A study was undertaken to determine the bond strength of brackets rebonded with a no-mix resin system or a paste-paste resin system. The efficacy of plastic conditioner and Enhance adhesion booster (Reliance Orthodontic Products, Inc., Itasca, Ill.) as an aid in rebonding was also evaluated. Sixty extracted human premolars were divided into two groups based on the two adhesive systems used. Both groups of 30 were subdivided and (1) initial bond, (2) rebond, and (3) rebond using plastic conditioner and adhesion booster. Samples were stressed to bond failure using an Instron machine. Bond separation occurred in the majority of samples at the enamel/resin interface. Mean bond strengths ranged from 78.8 kg cm-2 for rebonding with a no-mix adhesive and no other conditioners, to 182.7 kg cm-2 for initial bonding using a paste-paste adhesive. Rebonding using a paste-paste adhesive with no other conditioners produced a bond strength statistically indistinguishable from initial bonding with either system. Plastic conditioner and adhesion booster failed to improve rebond strength. The data suggest that, given certain circumstances, rebonding is a viable option when a bracket has been debonded.

Bicuspid↗
PubMed1996

Levels of root resorption associated with continuous arch and sectional arch mechanics.

The purpose of this study was to evaluate differences in the extent of root resorption between continuous arch and sectional mechanics. Fifty-six persons with similar malocclusions requiring the extraction of four premolars were divided into two equal groups and treated with the two different techniques. Once the canines were retracted with sliding mechanics (continuous arch wire group) or with force driven retraction loops (sectional mechanics group), the anterior teeth were then retracted with 300 gm Sentalloy coil springs (GAC international, Central Islip, N.Y.). The extent of root resorption of the anterior teeth was evaluated radiographically. Both treatment groups exhibited the same levels of resorption indicating that the side effect of treatment may be due to individual variation and not to the "round tripping" of teeth so often assumed.

Adolescent↗
PubMed1994

Characteristics of animals adopted from an animal control center whose owners complied with a spaying/neutering program.

A study of 137 cats and 567 dogs received by and subsequently adopted from an animal control center was performed to determine characteristics of animals whose new owners subsequently complied with a prepaid spaying/neutering program. Four times as many dogs as cats were adopted. Females were adopted more frequently than males. Owners who adopted female cats were most likely to comply with the prepaid spaying/neutering program, followed, in order, by owners of male cats, owners of female dogs, and owners of male dogs. Most animals returned to the shelter were < 4 months old. Dogs suspected to be of mixed breeding that were > 4 months old were most likely to be adopted. Owners who adopted a female dog suspected to be of mixed breeding were more likely to have the dog spayed than were owners who adopted a female dog that appeared purebred.

Animal Welfare↗
PubMed1993

The effect of fixed and functional appliances on enamel decalcifications in early Class II treatment.

The presence of enamel decalcifications before and after early Class II treatment was examined on 41 subjects and 164 permanent first molars. No new demineralization areas were found in patients wearing only a removable appliance. Of the maxillary molars 6% displayed decalcifications in patients wearing a headgear only: whereas of patients wearing a headgear and biteplate 25% displayed enamel lesions. Eighteen percent of white spot lesions diagnosed before treatment had shown a "reversal phenomenon," whereby the enamel appeared normal after treatment. This process only occurred in the functional appliance group indicating that remineralization was better achieved with an appliance that was capable of being removed from the oral cavity.

Activator Appliances↗
PubMed1992

Diagnosis and treatment planning in orthodontics.

Orthodontic diagnosis and treatment planning topics either reflect the new technology available in the health fields or reiterate the older material that reemerges from generation to generation. Issues that are presented still display the dissatisfaction of their examiners in terms of frustration and equivocal results. Well-controlled prospective and retrospective studies require documented long-term evaluations to be clinically useful as an aid in diagnosis or formulation of treatment planning principles.

Cephalometry↗
PubMed1992

Delayed retraction utilizing ceramic brackets.

The purpose of this study was to evaluate clinically the delay in retraction utilizing ceramic orthodontic brackets versus stainless steel brackets. Twelve patients with Class II division 1 malocclusions requiring the extraction of maxillary first premolars were employed in the study. The following observations were obtained: 1. Retraction of all cuspids bonded with ceramic brackets displayed delayed retraction when compared to their stainless steel counterparts. 2. Over a 36 week period, teeth bonded with stainless steel brackets travelled 2mm farther or 1.8 times faster than those bonded with ceramic brackets.

Adolescent↗
PubMed1991

Effects of pHi and pHe on membrane currents recorded with the perforated-patch method from cultured chemoreceptors of the rat carotid body.

In this study we investigated the effects of intracellular pH (pHi) and extracellular pH (pHe) on whole-cell currents in cultured glomus cells of the rat carotid body and small, intensely fluorescent (SIF) cells of sympathetic ganglia. The use of the perforated-patch recording technique along with established methods of cytoplasmic acidification allowed us to carry out this study without greatly disturbing the cell's endogenous pH regulatory mechanisms. A reversible decrease in the outward K+ current (20-30%) was observed during acid loading of glomus (and SIF cells) using the K+/H+ ionophore nigericin (3 microM) and acetate (20 mM). A reversible decrease in the inward Na+ current was also observed in both cell types during nigericin application. Application of amiloride (0.1 mM) to the bathing solution inhibited recovery of the K+ current from an acid load implicating the Na+/H+ antiporter as a mechanism involved in pH homeostasis in glomus cells. A reversible decrease in K+ and Na+ currents was also observed during changes in pHe from 7.4 to 6.5. The effects of pHi on membrane currents, Ca2+ levels, and neurotransmitter release are discussed in the context of the role of glomus cells as primary transducers of chemosensory stimuli in arterial blood.

Acetates↗
PubMed1991

Effects of orthodontic attachments on the gingival health of permanent second molars.

The aim of this study was to evaluate the effect of cemented bands and enamel bonded attachments on the gingival health of second molars. In 23 patients the right upper and lower second molars were banded, while the left upper and lower second molars were bonded. The plaque index, the gingival index, and pocket depths were greater and statistically significant on the right side, indicative of increased inflammatory activity where bands were cemented. Once the appliances were removed, both areas returned to pretreatment levels.

Adolescent↗