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PubMed1970

Studies on thymus function. II. Cooperative effect of newborn and embryonic hemopoietic liver cells with thymus function.

Significant immunological restoration of 45-day old, neonatally thymectomized C3Hf mice was obtained by the cooperation of syngeneic newborn or embryonic hemopoietic liver cells with thymic function. Thymic function or cells alone are almost ineffective or restore approximately 10% of the animals. Newborn liver cells are effective in association with thymus grafts or humoral thymic function (thymoma grafts and thymus or thymomas in diffusion chambers). Embryonic liver cells are ineffective, even in large numbers, when associated with humoral thymic function. On the other hand, embryonic liver cells are effective in the cooperative effect only in association with viable thymus grafts, preferably syngeneic, whether the grafts were placed subcutaneously, intraperitoneally, or under the kidney capsule. Dispersed viable thymic cells are ineffective in association with embryonic liver cells. Cells capable of cooperating with humoral thymic function start to appear to embryonic liver by day 19-21 of gestation and are detectable until day 5-6 postbirth. Embryonic hemopoietic liver cells from 12 to 18 days of gestation contain cells capable of cooperation only with viable free thymus grafts and not with humoral thymic function. A prethymic cell population of partially differentiated cells of hemopoietic origin, insensitive to humoral activity of the thymus but requiring thymic stroma and traffic through the thymus is postulated to explain our results. This population of prethymic cells can become postthymic through this process and eventually develop into competent cells. Postthymic cells are characterized by their sensitivity to humoral activity of the thymus and by their wide distribution in the lymphohemopoietic tissues of newborn and young adult mice.

Animals↗

PubMed1982

In vitro effects of 4-hydroperoxycyclophosphamide on human immunoregulatory T subset function. I. Selective effects on lymphocyte function in T-B cell collaboration.

The alkylating agent cyclophosphamide may suppress or enhance immune responses in vivo but is inactive in vitro unless metabolized by microsomal enzyme activation. 4-hydroperoxycyclophosphamide (4-HC) is a synthetic compound that is spontaneously converted in aqueous solution to the active metabolites. In this report, we examined the in vitro sensitivity of functional human T cell subsets to 4-HC in a polyclonal B cell differentiation assay and in the generation of mitogen-induced suppressor cells for effector B cell function. Con A-induced T suppression of B cell differentiation is completely abrogated by a 1-h pretreatment of T cells at very low concentrations of between 10(-2) and 20 nmol/ml, whereas inducer T cell function is sensitive only to concentrations in greater than 40 nmol/ml. The effects of 4-HC on suppressor T cells appear to occur at concentrations that do not result in DNA cross-linking or decreased blastogenesis. Con A-induced T suppressors are generated from within the OKT4+, OKT8- subset and are sensitive to low-dose 4-HC only before activation, whereas differentiated suppressor cells are resistant to concentrations in greater than 80 nmol/ml. Low-dose 4-HC pretreatment of the B cell population results in abrogation of immunoglobulin secretion when treated B cells are cocultured with unfractionated T cells, however, this effect is completely reversible if pretreated B cells are cocultured with T cells devoid of suppressor activity. These results demonstrate that human presuppressor cells for B-effector function differentiate in response to Con A from the OKT4+, OKT8- subset and are exquisitely sensitive to low concentrations of CYP whereas mature suppressor and inducer functions are resistant to all but very high concentrations in vitro. The differential sensitivity of functional T and B cell subsets to 4-HC in vitro can be a very useful probe in dissecting immunoregulatory interactions with man.

B-Lymphocytes↗

PubMed1982

Immune response gene function correlates with the expression of an Ia antigen. II. A quantitative deficiency in Ae:E alpha complex expression causes a corresponding defect in antigen-presenting cell function.

A series of experiments were performed to explore the role of complementing major histocompatability complex (MHC)-linked immune response Ir genes in the murine T cell proliferative response to the globular protein antigen pigeon cytochrome c. The functional equivalence of I-E-subregion-encoded, structurally homologous E(a) chains from different haplotypes bearing the serologic specificity Ia.7 was demonstrated by the complementation for high responsiveness to pigeon cytochrome c of F(1) hybrids between low responder B 10.A(4R) (I-A (k)) or B 10.S (I-A(8)) mice and four low responder E(a)- bearing haplotypes. Moreover, this Ir gene function correlated directly with both the ability of antigen-pulsed spleen cells from these same F(1) strains to stimulate pigeon cytochrome c-primed T cells from B10.A or B10.S(9R) mice, and with the cell surface expression of the two-chain Ia antigenic complex, A(e):E(a), bearing the conformational or combinatorial determinant recognized by the monoclonal anti-Ia antibody, Y-17. The B 10.PL strain (H-2(u)), which expresses an Ia.7-positive I-E- subregion-encoded E(a) chain, failed to complement with B10.A(4R) or B10.S mice in the response to pigeon cytochrome c. However, (B10.A(4R) x B10.PL)F(1) and (B10.S x B10.PL)F(1) mice do express A(k)(e):E(u)(a) and A(8)(e):E(u)(a) on their cell surface, although in reduced amounts relative to A(k,s)(e):E(k,d,p,r)(a) complexes found in corresponding F(1) strains. This quantitative difference in Ia antigen expression correlated with a difference in the ability to present pigeon cytochrome c to B 10.A and B 10.S(9R) long-term T cell lines. Thus, (B10.A(4R) x B10.PL)F(1) spleen cells required a 10-fold higher antigen dose to induce the same stimulation as (B10.A(4R) x B10.D2)F(1) spleen cells. In addition, the monoclonal antibody, Y-17, which reacts with A(e):E(a) molecules of several strains, had a greater inhibitory effect on the proliferative response to pigeon cytochrome c of B10.A T cells in the presence of (B10.A(4R) X B10.PL)F(1) spleen cells than in the presence of (B10.A(4R) X B10.D2)F(1) spleen cells. These functional data, in concert with the biochemical and serological data in the accompanying report, are consistent with the molecular model for Ir gene complementation in which appropriate two-chain Ia molecules function at the antigen-presenting cell (APC) surface as restriction elements. Moreover, they clearly demonstrate that the magnitude of the T cell proliferative response is a function of both the concentration of nominal antigen and of the amount of Ia antigen expressed on the APC. Finally, the direct correlation of a quantitative deficiency in cell surface expression of an Ia antigen with a corresponding relative defect in antigen-presenting function provides strong independent evidence that the I-region-encoded Ia antigens are the products of the MHC-linked Ir genes.

Animals↗

PubMed1997

Cytokine-induced cytotoxic function expressed by lymphocytes of the innate immune system: distinguishing characteristics of NK and LAK based on functional and molecular markers.

Several molecular events are now identifiable during the activation, recognition, and killing by natural killer (NK) cells that are distinct from those differentiated in response to cytokines during the generation of lymphokine-activated killer (LAK) cells or during lymphocyte proliferation. Because LAK and MHC-unrestricted killing activities also include the prototypic NK targets as part of their broad recognition spectra, accurate identification of the complete function being studied is critical. In many publications, past and present, only NK-sensitive target cells were used (K562, Molt-4, others), and, therefore, the results do not necessarily indicate whether the effectors are NK or have differentiated into LAK cells. Such a consideration becomes critical when the effectors are grown in interleukin-2 (IL-2), and an attempt is made to define receptor recognition, signal transduction pathways, and specificity at the molecular level. In some instances, effector cells are likely to have stopped, therefore merely expressing NK activity, and have also acquired LAK function. The identified receptors may not have been unique to NK cells or NK function. Not until the targets employed are also confirmed to be NK sensitive, and the effectors do not kill NK-resistant targets can the results of molecular studies be proposed to represent aspects unique to NK. Reports of the use of IL-2-expanded NK clones are most likely providing data concerning the biology of LAK and not of classic NK. The classic NK activity surveying our blood apparently performs an important function, including the ability to respond rapidly to certain cytokines and to acquire additional functions and receptors for use in destroying a vast array of target cells. It is critical for scientists to appreciate the functional distinctions and to identify the molecules and pathways unique to each of these curious cytolytic systems.

Biomarkers↗

PubMed1996

Both loss-of-function and gain-of-function mutations in snf define a role for snRNP proteins in regulating Sex-lethal pre-mRNA splicing in Drosophila development.

The Drosophila snf gene encodes a protein with functional homology to the mammalian U1A and U2B" snRNP proteins. Studies, based on the analysis of three viable alleles, have suggested a role for snf in establishing the female-specific splicing pattern of the sex determination switch gene, sex-lethal. Here, we show that the non-sex-specific lethal null allele is required for female sex determination, arguing against the formal possibility that the viable alleles disrupt a function unrelated to snf's wild-type function. Moreover, we find snf is required for normal cell growth and/or survival, as expected for a protein involved in a cell-vital process such as RNA splicing. We also show that of the three viable alleles only one, snfJA2, is a partial loss-of-function mutation. The other two viable alleles, snf1621 and snfe8H, encode antimorphic proteins. We find the antimorphic proteins are mislocalized and correlate their mislocalization with their molecular lesions and mutant phenotypes. Finally, we provide genetic evidence that the antimorphic alleles interfere with the autoregulatory splicing function of the Sex-lethal protein. Based on these studies we suggest a model in which the snRNP protein, Snf, functions with Sex-lethal to block recognition of the regulated male-specific exon.

Alleles↗

PubMed2001

Prevalence [correction of prevalance] of functional blindness, visual impairment, and related functional deficits among elderly Mexican Americans.

BACKGROUND: This report describes the prevalence and correlates of functional blindness and visual impairment among older Mexican Americans, using data on 2800 respondents from the Hispanic Established Populations for the Epidemiological Study of the Elderly. METHODS: Bivariate and multivariate logistic regression analyses were used to examine the associations between corrected bilateral distant vision and sociodemographic characteristics, selected health conditions, self-reported health status, health care utilization, and functional dependence on the basis of assistance needed for basic and instrumental activities of daily living (ADLs). RESULTS: Using a modified Snellen test for distance visual acuity, 5% of older Mexican Americans were found to be functionally blind, and 13.5% were found to be visually impaired. Vision loss was significantly associated with older age, lower education, hypertension, diabetes, poor self-rated health, and hospitalization during the year prior to the interview. Over 50% of functionally blind subjects required assistance with at least one basic ADL, compared with 15% of those who were visually impaired and 8% of those who were not visually impaired. CONCLUSIONS: The prevalence of functional blindness in this sample of elderly Mexican Americans was higher than reported for the general elderly population, yet they also have higher rates of adequate vision because of the low prevalence of visual impairment. The results suggest a need for more research on the prevalence and impact of functional blindness and visual impairment on the health of older Mexican Americans.

Age Factors↗

PubMed2001

Severity of upper and lower extremity functional limitation: scale development and validation with self-report and performance-based measures of physical function. WHAS Research Group. Women's Health and Aging Study.

OBJECTIVES: To better understand disablement and transitions from impairment to disability, discrete valid measures of functional limitation are needed. This study reports the development and criterion-related validity of scales that quantify severity of upper and lower extremity functional limitation. METHODS: Data are from 3,635 cognitively intact community-dwelling women aged 65 years and older and 1,002 moderately to severely disabled participants in the Women's Health and Aging Study. Scales assessing severity of upper and lower extremity functional limitation were constructed from commonly available questions on functional difficulty. Criterion-related validity was evaluated with self-report and performance-based measures. RESULTS: The upper and lower extremity scales range from 0 to 6 and 0 to 9, respectively. Scale scores were well distributed in the disabled group and discriminated limitations in the broader community. For both scales, rates of difficulty for all ADL and IADL increased (p<.001) with increasing severity score, and percent able and mean performance on respective upper and lower extremity tasks decreased (p<.01). DISCUSSION: These scales, constructed from commonly used self-report measures of function, provide discrete measures of upper and lower functional limitation. Because these scales are distinct from measures of disability and impairment, their use should facilitate increased understanding of the disablement process.

Activities of Daily Living↗

PubMed1999

Condition severity and psychosocial functioning in pre-adolescents with spina bifida: disentangling proximal functional status and distal adjustment outcomes.

OBJECTIVE: To examine relations between condition severity and psychosocial functioning in 70 8- and 9-year-old pre-adolescents with spina bifida by testing several direct, indirect, and mediated effects models for proximal functional status and distal adjustment outcomes. METHODS: Proximal functional status outcomes (e.g., degree of involvement in activities, scholastic competence, athletic competence, attentional problems) and distal adjustment outcomes (e.g., behavior problems, social competence) were assessed with mother, father, and teacher report. Severity variables included spinal lesion level, spina bifida classification, shunt status, ambulation status, number of shunt surgeries, and two severity composites. RESULTS: Condition severity was associated with the proximal functional status outcomes across parent and teacher report. In contrast, no significant relationships were found between the severity parameters and distal adjustment outcomes. Findings supported a proximal effects model of condition severity as well as an indirect effects model (e.g., presence of a shunt-->less scholastic competence-->less social competence) and were consistent with recent theoretical formulations (e.g., Wallander & Varni, 1995). CONCLUSIONS: Disentangling proximal functional status outcomes and distal adjustment outcomes is critical in studies of condition severity and psychosocial functioning. We discuss clinical implications.

Adaptation, Psychological↗

PubMed1996

Pulmonary function measures as predictors and correlates of cognitive functioning in later life.

The relation between pulmonary function and cognitive functioning was investigated in a cohort of 3,036 Japanese-American men living in Hawaii. Pulmonary function, as indicated by forced expiratory volume in 1 second (FEV1), was measured at the baseline examination from 1965 to 1968. Cognitive function was assessed by the Cognitive Abilities Screening Instrument (CASI) test at least 23 years later (1991-1993). Baseline FEV1 was significantly correlated with follow-up CASI score (r = 0.22, p = 0.0001). Although the strength of the association was reduced by controlling for the effects of other factors, stepwise multiple linear regression showed that FEV1 during middle age was a significant predictor of CASI in later life, after taking into account the effects of age, education, stroke, sedentary job activity, nonmanual occupation, height, generation, and Japanese speaking ability. The mean CASI value was significantly greater for men whose FEV1 exceeded 2.8 liter compared with those whose FEV1 levels were in the lowest (<2.5 liters) quartile. Furthermore, the test on the effect of interaction between FEV1 and age was statistically significant (p = 0.0024), with subjects less than 55 years of age at the baseline examination showing a stronger direct association of FEV1 with CASI than the men aged 55 or older. These findings suggest that pulmonary function impairment may be associated with cognitive function impairment in later life.

Aged↗

PubMed1996

The effects of sevoflurane and isoflurane anesthesia on renal tubular function in patients with moderately impaired renal function.

Increasing evidence indicates that sevoflurane anesthesia does not impair renal function in healthy patients despite higher concentrations of plasma inorganic fluoride. However, whether sevoflurane further affects renal tubular function in patients with impaired renal function is not known. We compared the effect of sevoflurane anesthesia with that of isoflurane anesthesia on renal tubular function in patients with moderately impaired renal function. Fourteen patients with creatinine clearance between 10 and 55 mL/min were anesthetized with either sevoflurane or isoflurane using a semiclosed circuit system. Plasma inorganic fluoride concentrations and urine N-acetyl-beta-D-glucosaminidase (NAG), gamma-glutamyltranspeptidase (gamma-GTP), and beta 2-microglobulin (beta 2MG) excretions were measured up to post-anesthetic day 14. Although both the peak plasma inorganic fluoride concentrations and the areas under the curve of plasma inorganic fluoride concentration versus time were significantly greater in the sevoflurane group than in the isoflurane group, urine NAG, gamma-GTP, and beta 2MG excretions per day did not differ between the two groups. These results indicate that sevoflurane and isoflurane may have similar effects on the renal tubules in patients with moderately impaired renal function.

Acetylglucosaminidase↗

PubMedDate not supplied

Functional gain and length of stay for major rehabilitation impairment categories. Patterns revealed by function related groups.

This study evaluates the relationship of functional severity to patterns of functional gain and length of stay (LOS) for patients discharged from medical rehabilitation. It further compares differences in patterns between summed and Rasch transformed subscales of the Functional Independence Measure (FIM). Two different schemes of the FIM-Function Related Groups (FIM-FRGs) are used to define groups of patients who present with similar degrees of functional severity. The first scheme was developed using summed admission motor and cognitive FIM subscores (FIM-FRGs). The second scheme was developed by transforming these same motor and cognitive FIM subscores into logits (Logit FIM-FRGs), thus making FIM scores more equal-interval. The study included 32,494 patients who were discharged from 123 facilities that submitted data to the Uniform Data System for Medical Rehabilitation (UDSMR) and involved the separate evaluation of 18 different rehabilitation impairment categories. Motor FIM gain was calculated for each FRG in both schemes as the patient's discharge motor FIM score minus the admission motor FIM score. There were four patterns of motor FIM gain and two patterns of LOS across rehabilitation impairment. The most common pattern in both schemes was linear trend, for which median gains and LOS were highest for patients in the most disabled FRGs and lowest for patients in the least disabled FRGs. Gain patterns differed across impairment and across the two schemes. The motor FIM gain distributions provide clinicians with a range of typical functional outcomes for patients admitted to medical rehabilitation. This descriptive approach provides clinicians and administrators with a simple way to compare the motor FIM gain and LOS patterns of patients teated in local facilities with broad-based norms. This sample includes about one-quarter of rehabilitation facilities nationwide, thus representing population standards for facilities participating in the UDSMR. Suggestions are made on how to use these norms most appropriately for both facility and patient comparison.

Activities of Daily Living↗

PubMed2002

Low-volume exercise rehabilitation improves functional capacity and self-reported functional status of dialysis patients.

OBJECTIVE: The purpose of this study was to examine the effects of a program of low-volume exercise rehabilitation on the functional capacity and self-reported functional status of nonanemic dialysis patients. DESIGN: This was a controlled study in a clinical setting with a repeated measures design. Functional capacity and functional status were assessed before and after 12 wk of exercise rehabilitation or 12 wk of normal activity for two groups of dialysis patients. RESULTS: Mixed-model repeated measures analysis of variance revealed significant group by time interactions characterized by improvements for the exercise rehabilitation group alone in total walk, stair-climb, and stair-descent times of 15+/-5.8%, 22+/-11%, and 18+/-12% respectively. Self-reported walking speed, walking impairment-leg weakness, and walking impairment-shortness of breath were also observed to improve significantly for the exercise rehabilitation group alone by 15+/-13%, 25+/-11%, and 28+/-16%, respectively. CONCLUSION: Low-volume exercise rehabilitation can improve activity of daily living-related functional capacity and self-reported functional status of nonanemic dialysis patients.

Activities of Daily Living↗

PubMed2000

A brief assessment of psychosocial functioning of subjects with bipolar I disorder: the LIFE-RIFT. Longitudinal Interval Follow-up Evaluation-Range Impaired Functioning Tool.

Those afflicted with bipolar disorder often suffer from substantial functional impairment both when in episode and when in remission. This study examined the psychometric properties of a brief assessment of psychosocial functioning, the Range of Impaired Functioning Tool (LIFE-RIFT), among subjects with bipolar I disorder. The study sample consisted of 163 subjects who presented with bipolar I disorder at intake into the NIMH Collaborative Depression Study (CDS). All LIFE-RIFT items come from the Longitudinal Interval Follow-up Evaluation (LIFE). Follow-up data that were used to examine the reliability and validity of the scale come from assessments of psychosocial functioning that were conducted 6, 12, 18, and 24 months after intake into the CDS. The results of factor analyses indicate that the scale items are measures of one construct, psychosocial functioning. The interrater agreement on the scale score was very good with an intraclass correlation coefficient was 0.94. The internal consistency reliability among the scale items was uniformly satisfactory over the four assessment periods, with coefficient alpha ranging from 0.78 to 0.84. Mixed-effect regression analyses showed that during mood episodes subjects were significantly more impaired than those in recovery. In conclusion, the psychometric properties of the LIFE-RIFT were examined in subjects with bipolar I disorder. The analyses from this longitudinal, observational study provide empirical support for the reliability and validity of the scale. The LIFE-RIFT provides a brief, inexpensive alternative to scales currently used to assess psychosocial functioning and can be easily added to semistructured assessments that are used in clinical and treatment outcome studies.

Adaptation, Psychological↗

PubMed2002

Executive function in schizophrenia: is it linked to psychosis and poor life functioning?

The authors examined the relationship of major aspects of executive function to acute psychosis and long-term outcome in patients enrolled in a 15-year study of the natural history of psychosis. They evaluated 157 patients, including 42 schizophrenic, 42 other psychotic, and 73 nonpsychotic psychiatric patients 15 years after index hospitalization. Patients were administered the Wisconsin Card Sorting Test (WCST) and measures of psychosis and posthospital adjustment. Schizophrenia patients performed significantly worse than both nonschizophrenic psychiatric control groups on WCST indices, regardless of psychosis. Aspects of executive function were impaired in schizophrenia patients with severe deficits in their level of overall functioning and outcome and also in many with only moderate impairment in overall functioning; however, these deficits were seen to a greater degree in schizophrenia patients with very poor overall functioning. Executive function deficits appear to be a core component of schizophrenia rather than an effect of acute psychotic disorganization, and are associated with long-term outcome.

Activities of Daily Living↗

PubMed2003

Pancreatic endocrine and exocrine function and salivary gland function in autoimmune pancreatitis before and after steroid therapy.

INTRODUCTION: Autoimmune pancreatitis (AIP) is a distinct clinical entity in which an autoimmune mechanism may be involved in pathogenesis. AIM: To investigate salivary gland function in addition to pancreatic endocrine and exocrine function in patients with AIP, and to determine changes occurring after steroid therapy. METHODOLOGY: Fasting serum glucose levels, oral glucose tolerance tests or glycosylated hemoglobin values were examined in 19 patients with AIP. N-benzoyl-L-tyrosyl-p-aminobenzoic acid excretion test, sialochemistry and parotid gland scintigraphy were performed in 8 patients. RESULTS: Eight patients had evidence of DM. Steroid therapy subsequently improved insulin secretion and glycemic control in 3 of 5 patients treated. Pancreatic exocrine function was reduced in 88% of patients. Impaired pancreatic exocrine function improved after steroid therapy in 3 of 6 patients treated. The 3 patients also showed treatment-related improvement in endocrine function. Concentration of beta2-microglobulin in saliva was significantly raised in patients with AIP compared with controls (P < 0.05). Ratio of cumulative peak count to injected radionuclide and washout ratio in parotid scintigraphy in patients with AIP was significantly lower than those of controls (P < 0.01). Salivary gland dysfunction improved after steroid therapy in all 5 patients treated. CONCLUSIONS: Pancreatic endocrine and exocrine and salivary gland function were frequently impaired in patients with AIP, and steroid therapy was occasionally effective for these dysfunctions.

Adult↗

PubMed2004

Alleviated tension at the repair site enhances functional regeneration: the effect of full range of motion mobilization on the regeneration of peripheral nerves--histologic, electrophysiologic, and functional results in a rat model.

BACKGROUND: In the clinical management of combined tendon and nerve injuries, competing treatment strategies are well known. The effect of mobilization on the functional regeneration of peripheral nerves remains controversial. This study sought to determine the effect of full range of motion mobilization on nerve repair by using tubular segmental nerve splinting to block movement, and thereby variable tension, at the nerve repair site. METHODS: In 96 rats, the right sciatic nerve was transected midthigh and coapted immediately microsurgically. The groups used in the study were as follows: group N, epineural nerve repair; group T, segmental tubular nerve splinting with fixed in situ tension at the nerve suture site,allowing segmental movement only; group TN, segmental tubular nerve splinting with alleviated in situ tension at the nerve suture site, allowing segmental movement only; and group TM, segmental tubular nerve splinting without fixed in situ tension at the nerve suture site, allowing movement of the nerve suture site. Full range of motion of the lower limbs was ensured by passive motion of hind limbs once a week after functional testing. Blinded histologic, immunohistochemical, and electrophysiologic assessment and 12 postoperative weekly function tests were carried out. RESULTS: Functional and electrophysiologic results were significantly better in group TN, by segmental tubular nerve splinting with alleviated in situ tension at the nerve repair site, mainly because of less scar formation and enhanced endoneural angiogenesis at the nerve suture segment. CONCLUSION: Full range of motion mobilization may impede functional nerve recovery by significant endoneural collagenization and decreased angiogenesis at the nerve suture segment. Complete alleviation of in situ (pathophysiologic) tension at the nerve suture site seems to improve functional peripheral nerve regeneration.

Animals↗

PubMed2003

nth-Nearest-neighbor distribution functions of an interacting fluid from the pair correlation function: a hierarchical approach.

The paper presents a general formalism for the nth-nearest-neighbor distribution (NND) of identical interacting particles in a fluid confined in a nu-dimensional space. The nth-NND functions, W(n,r) (for n=1,2,3, em leader) in a fluid are obtained hierarchically in terms of the pair correlation function and W(n-1,r) alone. The radial distribution function (RDF) profiles obtained from the molecular dynamics (MD) simulation of Lennard-Jones (LJ) fluid is used to illustrate the results. It is demonstrated that the collective structural information contained in the maxima and minima of the RDF profiles being resolved in terms of individual NND functions may provide more insights about the microscopic neighborhood structure around a reference particle in a fluid. Representative comparison between the results obtained from the formalism and the MD simulation data shows good agreement. Apart from the quantities such as nth-NND functions and nth-nearest-neighbor distances, the average neighbor population number is defined. These quantities are evaluated for the LJ model system and interesting density dependence of the microscopic neighborhood shell structures are discussed in terms of them. The relevance of the NND functions in various phenomena is also pointed out.

Journal Article↗

PubMed1993

The asymmetric regions of rotation functions between Patterson functions of arbitrarily high symmetry.

Rotation functions between Patterson functions can be calculated and analyzed more efficiently when it is possible to consider only a unique or asymmetric region of rotation space. Previous authors have succeeded in characterizing the symmetries and asymmetric units of rotation functions between Patterson functions whose symmetries are less than cubic. Here we describe a simple and general solution that applies to rotation functions between Patterson functions of any symmetry, including cubic. The method relies on partitioning rotation space into Dirichlet domains.

Chemistry, Physical↗