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At least 865 records · Page 48Linked to original sources
PubMed2004

Neonatal tolerance revisited again: specific CTL priming in mouse neonates exposed to small numbers of semi- or fully allogeneic spleen cells.

Neonatal and adult mice mount distinct responses to allogeneic cells. Injection of neonates with fully allogeneic cells results in lethal graft-vs.-host disease (GVHD), whereas injection of semi-allogeneic (F1) cells leads to lifelong tolerance to the alloantigens, often marked by specific CTL non-responsiveness. In contrast, adults injected with the same number of either cell type become primed and develop vigorous anti-donor CTL activity. One possibility for this differential responsiveness may be developmental immaturity in the CTL arm of the immune system. Recent studies have shown that neonates are capable of mounting mature CTL responses, but only in the presence of strong Th1-promoting agents. Here, we demonstrate that neonates are competent to develop vigorous MHC class I-restricted CTL activity in vivo upon exposure to either fully or semi-allogeneic spleen cells. Specific CTL activity was generated using doses of cells approximately tenfold lower than levels used for the induction of GVHD or tolerance. Thus, the present studies demonstrate that mouse neonates are fully mature in their capacity to develop alloreactive CTL activity, as long as the dose of donor cells is low enough. These results have important implications for the known exposure of human fetuses and infants to small numbers of maternal cells.

Animals↗
PubMed1991

Retinal neurite growth on astrocytes is not modified by extracellular matrix, anti-L1 antibody, or oligodendrocytes.

Two factors that may influence the course of axonal regeneration in the central nervous system (CNS) are extracellular matrix (ECM) and cell surface molecules that may enhance or inhibit neurite outgrowth. Whereas cultured astrocytes have been reported to be a good substratum for neurite outgrowth, there is recent evidence that cultured oligodendrocytes are inhibitory. To test the influences of 1) ECM components, 2) the L1 adhesion molecule, and 3) the inhibitory potential of mature oligodendrocytes in the astrocytic environment, we have utilized a culture system in which neurites from embryonic rat retina grow vigorously on astrocyte monolayers. The major ECM components were assembled in neonatal rat cortical astrocyte-retina co-cultures only when the medium contained serum. In electron microscopic studies of serum containing cultures, retinal neurites were seen to be related to astrocyte surfaces but rarely were found in contact with ECM; in serum-free medium the association between neurites and astrocytes was similar. In addition, the growth of neurites was vigorous whether ECM was present or absent. Presence of antibodies against the cell surface adhesion molecule L1 did not inhibit retinal neurite elongation on glial fibrillary acidic protein-positive astrocytes. When oligodendrocytes from adult rat spinal cord were combined with the astrocytes, retinal neurites grew as well on the mixed glial population as on astrocytes alone. Immunostaining for galactocerebroside showed many oligodendrocyte processes to be aligned in the direction of neurite growth, suggesting association between the two cell types. This association was verified by electron microscopy. Furthermore, retinal explants extended neurites among myelin basic protein-positive oligodendrocytes cultured without astrocytes. Thus, the astrocyte surface is a strong promoter of neurite growth from embryonic rat retina. This growth did not depend upon either ECM or the L1 adhesion molecule. Because neurites grew on astrocytes in the presence of mature oligodendrocytes or among oligodendrocytes alone, we conclude that oligodendrocytes do not inhibit neurite growth under certain conditions.

Animals↗
PubMed1984

The incidence of hypercalcemia in squamous cell carcinoma of the head and neck.

Hypercalcemia is a well-recognized phenomenon in squamous cell carcinoma of the head and neck, but the incidence of hypercalcemia in this group of patients is not clear. We have reviewed the records of 166 patients with squamous cell carcinoma of the head and neck presented at the Boston VA Medical Center over a 2-year period (October 1981 to September 1983). Hypercalcemia (greater than 11 mg/dl), for which a benign etiology could not be identified, occurred in the clinical course of seven patients (4.2%). Of the hypercalcemic patients, 5/7 (71.4%) had advanced stage IV disease and serum calcium levels ranging from 11.2 to 15 mg/dl at presentation. The incidence of hypercalcemia in this stage IV group was 5/78 (6.4%). On the basis of concomitant serum alkaline phosphatase, x-ray films, and radionuclide bone scans in these patients, bone metastases or a humoral factor were felt to be the etiologic agent. Six of the seven patients died within 77 days of the onset of the hypercalcemia despite vigorous antihypercalcemic and chemotherapeutic measures, and the remaining patient is under chemotherapy at present. We conclude that hypercalcemia is a late manifestation of advanced squamous cell carcinoma of the head and neck and is an ominous prognostic sign. Hypercalcemia without bone metastases is presumably due to the production of ectopic parathormone (PTH)-like substances from the tumor. To control this hypercalcemia, the underlying tumor must be treated vigorously in conjunction with symptomatic treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2006

Physical activity and lung cancer risk in the European Prospective Investigation into Cancer and Nutrition Cohort.

Research conducted predominantly in male populations on physical activity and lung cancer has yielded inconsistent results. We examined this relationship among 416,277 men and women from the European Prospective Investigation into Cancer and Nutrition (EPIC). Detailed information on recent recreational, household and occupational physical activity, smoking habits and diet was assessed at baseline between 1992 and 2000. Relative risks (RR) were estimated using Cox regression. During 6.3 years of follow-up we identified 607 men and 476 women with incident lung cancer. We did not observe an inverse association between recent occupational, recreational or household physical activity and lung cancer risk in either males or females. However, we found some reduction in lung cancer risk associated with sports in males (adjusted RR = 0.71; 95% confidence interval 0.50-0.98; highest tertile vs. inactive group), cycling (RR = 0.73; 0.54-0.99) in females and non-occupational vigorous physical activity. For occupational physical activity, lung cancer risk was increased for unemployed men (adjusted RR = 1.57; 1.20-2.05) and men with standing occupations (RR = 1.35; 1.02-1.79) compared with sitting professions. There was no evidence of heterogeneity of physical activity associations across countries, or across any of the considered cofactors. For some histologic subtypes suggestive sex-specific reductions, limited by subgroup sizes, were observed, especially with vigorous physical activity. In total, our study shows no consistent protective associations of physical activity with lung cancer risk. It can be assumed that the elevated risks found for occupational physical activity are not produced mechanistically by physical activity itself but rather reflect exposure to occupation-related lung cancer risk factors.

Adult↗
PubMed1997

Physical activity and physical fitness in African-American girls with and without obesity.

Lack of physical activity and low levels of physical fitness are thought to be contributing factors to the high prevalence of obesity in African-American girls. To examine this hypothesis, we compared habitual physical activity and physical fitness in 54 African-American girls with obesity and 96 African-American girls without obesity residing in rural South Carolina. Participation in vigorous (> or = 6 METs) (VPA) or moderate and vigorous physical activity (> or = 4 METs) (MVPA) was assessed on three consecutive days using the Previous Day Physical Activity Recall. Cardiorespiratory fitness was assessed using the PWC 170 cycle ergometer test. Upper body strength was determined at two sites via isometric cable tensiometer tests. Relative to their counterparts without obesity, girls with obesity reported significantly fewer 30-minute blocks of VPA (0.90 +/- 0.14 vs. 1.3 +/- 0.14) and MVPA (1.2 +/- 0.18 vs. 1.7 +/- 0.16) (p < 0.01). Within the entire sample, VPA and MVPA were inversely associated with body mass index (r = -0.17 and r = -0.19) and triceps skinfold thickness (r = -0.19 and r = -0.22) (p < 0.05). In the PWC 170 test and isometric strength tests, girls with obesity demonstrated absolute scores that were similar to, or greater than, those of girls without obesity; however, when scores were expressed relative to bodyweight, girls with obesity demonstrated significantly lower values (p < 0.05). The results support the hypothesis that lack of physical activity and low physical fitness are important contributing factors in the development and/or maintenance of obesity in African-American girls.

Black People↗
PubMed1987

Fluorescence lifetime measurements using total internal reflection fluorimetry: evidence for a conformational change in albumin adsorbed to quartz.

We have modified the total internal reflectance fluorimetry (TIRF) method to determine, indirectly, quantum fluorescence yield and thus infer structural changes of adsorbed plasma proteins. We employed a frequency multiplied Nd:YAG pulse laser to excite tryptophan residues of bovine serum albumin (BSA), measuring the resulting fluorescence lifetimes. BSA adsorbed on quartz was investigated at normal pH and under acidic (pH 3.8) conditions at which albumin shape change has been established in bulk solution. Albumin adsorbed at pH 7.2 has a slightly lower lifetime than the bulk solution value, reflecting a population of both native and isomerized forms. Gently washing the adsorbate surface significantly reduces fluorescence lifetime, suggesting retention of more tenacious, conformationally altered molecules. Vigorous washing further reduces fluorescence lifetimes to values close to those obtained in bulk under acidic conditions. Similar alterations in fluorescence lifetimes were observed for heat-denatured albumin. These results support the hypothesis that adsorbed albumin exists in the form of a two-layer deposit, each with a possibly different structure. A loosely held layer, consisting of BSA microaggregates and including partially unfolded molecules, exists on the undisturbed surface and is partially removed by gentle washing. Vigorous washing removes all but the most tightly held protein, which exists in a possibly further unfolded configuration. The decrease in fluorescence lifetime of adsorbed BSA implies a corresponding change in quantum yield. A change in quantum yield of BSA tryptophan fluorophors implies that measuring adsorbed protein concentration by intrinsic fluorescence is unreliable.

Adsorption↗
PubMed1996

The effect of weight-bearing exercise on bone mineral density: a study of female ex-elite athletes and the general population.

The aim of this retrospective cohort study was to estimate the changes in bone mineral density (BMD) as a consequence of exercise in female ex-athletes and age-matched controls. Eighty-three ex-elite female athletes (67 middle and long distance runners, 16 tennis players, currently aged 40-65) were recruited from the original records of their sporting associations. Controls were 585 age-matched females. The main outcome measures were BMD of lumbar spine (LS), femoral neck (FN), and forearm, estimated by dual-energy X-ray absorptiometry (DXA) scan. Levels of physical activity were assessed using a modified Allied Dunbar Fitness Survey scale and classified as (a) ex-athletes, (b) active controls (> or = 1 h of vigorous physical activity currently and in the past), (c) low activity controls with inconsistent or intermediate levels of activity, and (d) inactive controls (< 15 minutes of exercise per week). After adjustment for differences in age, weight, height, and smoking, athletes had greater BMDs than controls: 8.7% at the LS (95% confidence interval [CI] 5.4-12.0; p < 0.001) and 12.1% at FN (CI 9.0-15.3; p < 0.001). The benefits of exercise appeared to persist after cessation of sporting activity. Active controls (n = 22) had greater BMDs than the inactive group (n = 347): 7.9% LS (CI 2.0-13.8; p = 0.009) and 8.3% FN (CI 2.7-13.8; p = 0.004). The low activity controls (n = 216) had an intermediate BMD. Tennis players had greater BMDs compared with runners: 12.0% LS (CI 5.7-18.2; p = 0.0004) and 6.5% FN (CI -0.2-13.2; p = 0.066). The BMD of tennis players' dominant forearms were greater than their nondominant forearms. In conclusion, regular vigorous weight-bearing exercise of 1 h or more per week is associated with an increase in BMD within a normal population. This study confirms long-term weight-bearing exercise as an important factor in the regulation of bone mass and fracture prevention.

Absorptiometry, Photon↗
PubMed1993

Accumulation of insulin-like growth factor binding protein-3 in conditioned medium of human fibroblasts increases with chronologic age of donor and senescence in vitro.

We have found that insulin-like growth factor binding protein-3 (IGFBP-3) accumulates to higher levels in medium conditioned by a strain of normal fibroblasts at late passage (LP) and a strain derived from subjects with Werner syndrome (WS) of premature aging, compared to medium conditioned by the same normal cells at early passage (EP) (Goldstein et al., Proc. Natl. Acad. Sci. USA, 88:9680-9684, 1991). To explore the generality of this phenomenon with respect to chronological age of donor (in vivo aging) and LP (in vitro senescence) we assayed IGFBP-3 in medium conditioned by 18 normal fibroblast strains at EP and LP and two WS strains at the midpoint of their curtailed replicative lifespans and assessed IGFBP-3 mRNA levels in cells by Northern analysis. The lowest accumulations of IGFBP-3 were found in medium conditioned by fetal cells with progressively increasing amounts postnatally; direct correlations between IGFBP-3 levels and donor age were seen in EP cells 3 days after subculture (during logarithmic growth) r = 0.80, P < 0.001, and 7 days after subculture (at confluence) r = 0.77, P < 0.001. With two exceptions, conditioned medium of cell strains accumulated more IGFBP-3 at LP; IGFBP-3 levels correlated with chronological age after 3 days, r = 0.50, P = 0.05, and after 7 days, r = 0.75, P < 0.001. IGFBP-3 content of WS culture medium fell within the range of LP normal cells. Cumulative IGFBP-3 levels were inversely proportional to the thymidine labeling index, a measure of proliferative vigor. With some exceptions IGFBP-3 mRNA levels were commensurate with the amount of IGFBP-3 accumulated in the medium, suggesting that distal translational and posttranslational mechanisms also regulate IGFBP-3 production in some strains. The trend toward augmented IGFBP-3 output of fibroblasts as a direct function of chronological age and in vitro senescence and as an inverse function of proliferative vigor is consistent with the known inhibitory effect of excess IGFBP-3 on IGF-mediated DNA synthesis and the reduced regenerative potential that is evident during biological aging in vivo.

Aging↗
PubMed1982

Fertile life of acrosome-reacted guinea pig spermatozoa.

To study the fertile life of acrosome-reacted guinea pig spermatozoa, spermatozoa were induced to undergo a synchronous acrosome reaction after which vigorously motile acrosome-reacted spermatozoa were isolated from acrosome-intact ones. Acrosome-reacted spermatozoa thus prepared were incubated in vitro for various periods of time before they were mixed with zona-intact and zona-free eggs. Such spermatozoa retained their ability to fertilize zona-intact eggs for at least 2 hours after the acrosome reaction; thereafter they rapidly lost this ability. There was a close correlation between the decline and loss of the ability to penetrate the zona and the loss of hyperactivated motility by spermatozoa, indicating the importance of vigorous motility in passing through the zona. The ability of acrosome-reacted spermatozoa to fertilize zona-free eggs was maintained for many hours even after the spermatozoa had completely lost their capacity to fertilize zona-intact eggs. As long as acrosome-reacted spermatozoa are "alive," they seem to retain the capacity to fuse with the egg plasma membrane regardless of the quality of their motility.

Acrosome↗
PubMed2003

Moderate local and systemic respiratory syncytial virus-specific T-cell responses upon mild or subclinical RSV infection.

Respiratory syncytial virus (RSV) infections are a major cause of severe respiratory disease in infants. It has been shown that there is an increased frequency of childhood wheezing in ex-bronchiolitic preteen children. This was postulated to be mediated by a vigorous virus-specific Th2 response influencing the further development of the immune system. Little is known about the possible role of the immune response to clinically mild RSV infections in this respect. We have studied the RSV-specific cellular immune response in infants with a laboratory-confirmed RSV upper respiratory tract infection (URTI; n = 13, mean age 12 months, range 2-22 months) in comparison with infants with non-RSV mediated URTI (n = 9, mean age 9.3 months, range 4-18 months) or infants with severe RSV bronchiolitis (n = 11, mean age 2.3 months, range 1-6 months). RSV-specific cytokine-producing cells were enumerated using the ELISPOT method in peripheral blood mononuclear cells and nasal brush T-cells, collected during the acute and convalescent phase of the infection. Mixed Th1 (IFN-gamma) and Th2 (IL-4 and IL-13) responses were detected in all three groups. Frequencies of RSV-specific T-cells were lower in both URTI groups than in the RSV bronchiolitis group, and not significantly different between the RSV URTI and the non-RSV URTI group. The absence of vigorous virus-specific Th2 responses upon mild RSV infection does not support the hypothesis that these infections influence the development of the immune system and that they predispose for the development of atopic disease.

Cytokines↗
PubMed1988

Effect of irrigation and tourniquet application on aminoglycoside antibiotic concentrations in bone.

Preoperative antibiotics are an important measure taken to prevent infection in joint replacement surgery. The local availability of these antibiotics in the operative site is absolutely necessary to ensure adequate prophylaxis against contaminant bacteria. Because pulsatile-lavage rapid-recovery systems have become a routine technique of bone preparation in joint reconstruction, we chose to study the effect of these systems on local antibiotic concentrations. We further investigated the effect of irrigation with and without use of a limb tourniquet. For our study, we obtained 23 bone specimens in 16 patients undergoing joint reconstruction (14) or amputation (2). The patients were classified into one of four groups based on whether a tourniquet was applied during the procedure and whether the bone specimens were irrigated. In addition, matched blood samples were obtained to establish that therapeutic serum levels were achieved. Nine patients contributed 13 bone specimens, which underwent vigorous irrigation in vitro. None of these specimens had detectable levels of antibiotics, regardless of whether a tourniquet was used. Seven patients yielded 10 bone specimens, which were not irrigated. Five of these seven patients had detectable levels of antibiotics. In addition, the specimens from limbs without tourniquets had levels that averaged 0.51 microgram/ml while those with tourniquets averaged below 0.2 microgram/ml. Therefore, the use of vigorous irrigation in bone preparation has a significant deleterious effect on the local presence of previously administered systemic antibiotics. This effect is compounded if the operative site is isolated from continuous blood flow by use of a tourniquet. We therefore recommend that additional measures be taken to ensure that adequate antibiotic levels are present.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1999

Vocal recognition in the spotted hyaena and its possible implications regarding the evolution of intelligence.

Spotted hyaenas, Crocuta crocuta, are gregarious carnivores whose social lives share much in common with those of cercopithecine primates. We conducted playback experiments to determine whether free-living hyaenas are capable of identifying individual conspecifics on the basis of their long-distance vocalization, the 'whoop'. When prerecorded cub whoops were played to mothers and other breeding females (controls), mothers responded significantly more vigorously to whoops of their own cubs than did controls. We also tested the hypothesis that specific vocal recognition abilities are based on kinship in this species. Listeners that were related to the whooping cub responded more vigorously to recorded vocalizations than did unrelated individuals, with response intensity in some cases increasing directly with the size of the coefficient of relatedness (r). Our final goal was to determine whether control animals in these experiments can recognize third-party social relationships among other group members, an ability demonstrated by vervet monkeys, Cercopithecus aethiops, in similar playback experiments conducted by earlier investigators. In contrast to vervets, control females in the present experiments were no more likely to look at the mother of the whooping cub than at other control females after playback. This suggests that hyaenas may accomplish many of the same social feats as do vervets without possessing the ability to recognize third-party relationships. If confirmed in other domains of hyaena social life, our findings have important implications regarding selection pressures favouring the evolution of intelligence. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1994

Antibodies to murine CD40 protect normal and malignant B cells from induced growth arrest.

We have previously described the production of polyclonal anti-murine CD40 antibodies that specifically bind recombinant murine CD40 expressed on L cells and induce vigorous proliferation of normal murine B lymphocytes. The current study utilizes these antibodies to explore the distribution and function of CD40 in murine B cell development. Murine CD40 is expressed at high levels by normal splenic B cells and all Ig-positive B cell lymphomas tested to date. It is not expressed by the 70Z/3 pre-B cell line, BaF3 pre-B cell line, or by numerous T cell and myeloid cell lines. 70Z/3 pre-B cells can be induced to express CD40 by LPS stimulation of the cells. Stimulation of purified splenic B cells with anti-CD40 antibodies causes upregulation of class II MHC antigens, CD23, and ICAM-1 and results in extensive aggregation of the cells. Antibodies to murine CD40 are extremely effective at rescuing malignant and normal B cells from induced growth arrest. Anti-CD40 antibodies protect WEHI-231 and CH31 B lymphoma cells from growth arrest induced by soluble anti-IgM antibodies, TGF beta, or a combination of both stimulants. Similarly, anti-IgM preactivated normal splenic B cells which normally die rapidly from growth arrest after 1 or 2 days culture produce a vigorous proliferative response to subsequent stimulation with anti-CD40 antibodies plus IL-4. Interestingly, anti-CD40 antibodies provide little to no protection against B lymphoma growth arrest induced by immobilized anti-IgM antibodies. These data confirm and extend functional properties assigned previously to human CD40 and identify numerous defined murine model systems to explore the molecular basis of CD40-mediated protection from induced B cell growth arrest.

Animals↗
PubMed2001

Effects of Long-Term Video-electroencephalographic Monitoring on Mood in Epilepsy Patients.

This study examines changes in mood of 79 epilepsy patients who completed the Profile of Mood States during long-term video-electroencephalographic monitoring (LTM). Statistical linear models included the effects of age, gender, increased seizure frequency, sleep deprivation, and taper of antiepileptic drugs (AEDs) on mood. Sleep deprivation increased fatigue and decreased vigor from baseline to Day 3, but not from baseline to Day 8 or the final day of the protocol. Taper of AEDs did not adversely affect mood, with removal of phenytoin improving mood. Subjects who had seizures during LTM also improved in mood, becoming less depressed and less fatigued than those who did not have seizures. Overall, our data indicate that LTM does not adversely affect mood. However, in the first few days of LTM, sleep deprivation may produce fatigue and lack of vigor, and should be used only as needed to provoke seizures.

Journal Article↗
PubMed2000

Measuring the health of the Chesapeake Bay: toward integration and prediction.

The health of an ecosystem is a function of its vigor (useful productivity), organization (complexity of interspecific interactions), and resilience (ability to maintain itself in the face of disturbance). The health of the Chesapeake Bay ecosystem has deteriorated largely as a result of nutrient overenrichment, concomitant reduction in light availability, and loss of habitats that provide complexity. This has resulted in an ecosystem that is a less vigorous producer of valuable fish and shellfish, less diverse and well organized, and more susceptible to and slower to recover from disturbances. It is not clear that degraded ecosystem health directly threatens human health; in fact sanitation and reductions in loadings of potentially toxic substances have reduced human health risks in recent decades. On the other hand, recently observed outbreaks of the toxin-producing dinoflagellate Pfiesteria piscicida could be a result of deteriorated ecosystem health and pose a human health risk. Monitoring of the environmental conditions, ecosystem health, and human health risks is critically important to the adaptive management of the Chesapeake Bay. Although this monitoring has produced very useful information, monitoring can be more effective if it more directly addressed the multiple uses of the resulting information, applied new technologies, and were more effectively integrated across environmental media, among resources, over space and time scales, and with modeling and research.

Animals↗
PubMed1998

Immunization of diabetes-prone or non-diabetes-prone mice with GAD65 does not induce diabetes or islet cell pathology.

Glutamic acid decarboxylase autoimmunity was investigated by immunizing female BALB/c, C57B1/6, National Marine Research Institute (NMRI) and non-obese diabetic (NOD) mice once or twice with glumatic acid decarboxylase, GAD65, bovine serum albumin, or phosphate-buffered saline in incomplete Freunds adjuvant, or not treating. Mice immunized with GAD65, showed splinic T-cell reactivity to GAD 65 in vitro assessed by cytokine secretion. However untreated NOD mice did not. NOD mice showed a vigorous IFN-gamma response after one immunization, whereas NMRI mice showed a lower response. IL-4 and IL-10 were only detected after two immunizations with higher levels in BALB/c, NMRI and NOD mice, compared to C57B1/6 mice. High levels of GAD65 antibodies were detected in all mice immunized with GAD65, though lower levels were found in C57B1/6 mice. Histological analysis of pancreata revealed that no control mice, regardless of treatment, had mononuclear cell infiltration in the islets. In NOD mice, peri-insulitis was detected in all groups, but less so in GAD65 and bovine serum albumin (BSA) immunized animals. These data demonstrate that NOD mice respond more vigorously to immunization with GAD65 than non-diabetic mice strains. Furthermore, immunization with GAD65 is not sufficient to provoke onset of diabetes in NOD mice or induce islet cell pathology in non-diabetes prone mice.

Animals↗
PubMed1998

Effect of Long Chain Alcohols on Micellar Relaxation Time and Foaming Properties of Sodium Dodecyl Sulfate Solutions.

The effect of long chain alcohols (5 mol% CnOH for n = 8, 10, 12, 14, and 16) on the micellar stability of sodium dodecyl sulfate (SDS) solutions (SDS concentration ranging from 25 to 200 mM) was investigated and related to foaming properties, such as foamability, dynamic and equilibrium surface tension, and surface viscosity. The slow micellar relaxation time tau2, which is directly related to micellar stability, was determined by the pressure-jump technique. It was found that below 150 mM all the long chain alcohols investigated in this study cause an increase in tau2 and, hence, micellar stability, due to the strong ion-dipole interaction between the SDS and the alkyl alcohol. However, above approximately 150 mM SDS, all alcohols except C12OH decrease the micellar stability due to mismatching of the alkyl chains. When the chain length of the alcohol and SDS are not equal, the excess hydrocarbon chain exhibits thermal motion, thereby increasing the area per molecule in micelles as well as at the air/water interface. Foamability was determined by two methods: air blowing through a single capillary submerged in the surfactant solution or vigorous hand shaking. When enough time is allowed for the interface to form (in case of single bubble foam generation), the dynamic surface tension approaches the equilibrium surface tension. Since the equilibrium surface tension for the SDS/C12OH mixture is significantly lower (approximately 7 mN/m) than that for the pure SDS solution, more foam is generated with the mixed surfactant system. However, in very high shear rate processes (e.g., vigorous hand shaking), the break up time of micelles determines the flux of surfactant molecules to the interface and hence the foamability. Since the mixed SDS/C12OH micelles are more stable (longer relaxation time, tau2) than pure SDS micelles, higher dynamic surface tensions are attained and thus less foam is generated with the surfactant/alcohol mixture by the shaking method. In conclusion, we show that the foamability can exhibit opposite behavior depending upon the rate of foam generation (i.e., specific method used for foaming). Copyright 1998 Academic Press.

Journal Article↗
PubMed2000

Mathematical elements of attack risk analysis for mountain pine beetles.

Three different mathematical approaches are combined to develop a spatial framework in which risk of mountain pine beetle (MPB) attack on individual hosts may be assessed. A density-based partial differential equation model describes the dispersal and focusing behavior of MPB. A local projection onto a system of ordinary differential equations predicts the consequences of the density equations at individual hosts. The bifurcation diagram of these equations provides a natural division into categories of risk for each host. A stem-competition model links host vigor to stand age and demographics. Coupled together, these models illuminate spatial risk structures which may also shed light on the role of climatic variables in population outbreaks. Preliminary results suggest that stand microclimate has much greater influence on risk of attack than host vigor and stand age.

Animals↗