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Beam-beam limit in e+e- circular colliders.

Beam-beam effects limit the luminosity of circular colliders. Once the bunch population exceeds a threshold, the luminosity increases at a slower rate. This phenomenon is called the beam-beam limit. Onset of the beam-beam limit has been analyzed with various simulation methods based on the weak-strong and strong-strong models. We have observed that an incoherent phenomenon is mainly concerned in the beam-beam limit. The simulation have shown that equilibrium distributions of the two colliding beams are distorted from Gaussians when the luminosity is limited. The beam-beam limit is estimated to be xi approximately 0.1 for a B factory with damping time of several thousand turns.

Journal Article↗

Effects of Iron Limitation on Photosystem II Composition and Light Utilization in Dunaliella tertiolecta.

The effects of iron limitation on photosystem II (PSII) composition and photochemical energy conversion efficiency were studied in the unicellular chlorophyte alga Dunaliella tertiolecta. The quantum yield of photochemistry in PSII, inferred from changes in variable fluorescence normalized to the maximum fluorescence yield, was markedly lower in iron-limited cells and increased 3-fold within 20 h following the addition of iron. The decrease in the quantum yield of photochemistry was correlated with increased fluorescence emission from the antenna. In iron-limited cells, flash intensity saturation profiles of variable fluorescence closely followed a cumulative one-hit Poisson model, suggesting that PSII reaction centers are energetically isolated, whereas in iron-replete cells, the slope of the profile was steeper and the calculated probability of energy transfer between reaction centers increased to >0.6. Immunoassays revealed that in iron-limited cells the reaction center proteins, D1, CP43, and CP47, were markedly reduced relative to the peripheral light-harvesting Chl-protein complex of PSII, whereas the [alpha] subunit of cytochrome b559 was about 10-fold higher. Spectroscopic analysis established that the cytochrome b559 peptide did not contain an associated functional heme. We conclude that the photochemical conversion of absorbed excitation energy in iron-limited cells is limited by the number of photochemical traps per unit antenna.

Journal Article↗

A 36 Kilodalton Limiting-CO(2) Induced Polypeptide of Chlamydomonas Is Distinct from the 37 Kilodalton Periplasmic Carbonic Anhydrase.

Chlamydomonas reinhardtii possesses a CO(2)-concentrating mechanism, induced by limiting CO(2), which involves active transport and accumulation of inorganic carbon within the cell. Synthesis of several proteins is induced by limiting CO(2), but, of those, only periplasmic carbonic anhydrase has an identified function in the system. No proteins involved in active transport have yet been identified, but induced, membrane-associated polypeptides, such as the 36 kilodalton polypeptide focused on in this paper, would seem to be candidates for such involvement. The 36 kilodalton polypeptide was shown to be synthesized de novo upon transfer of cells to limiting CO(2). It was purified using SDS-PAGE and used to produce polyclonal antibodies. Antibodies were used to confirm the air-specific nature of the polypeptide, its strict association with membrane fractions, and the time course of its induction. Using the antibodies, a single, 36 kilodalton polypeptide was found to be specifically immunoprecipitated from in vitro translation products of poly(A(+)) RNA from cells only after exposure to limiting CO(2). The absence of translatable mRNA for this polypeptide in CO(2)-enriched cells indicated that regulation occurs at the level of message abundance. The antibodies were also used to demonstrate the distinction between the limiting-CO(2) induced 36 kilodalton polypeptide and the similarly sized, limiting-CO(2) induced periplasmic carbonic anhydrase.

Journal Article↗

Effects of Phosphorus Limitation on Respiratory Metabolism in the Green Alga Selenastrum minutum.

The effects of phosphorus nutrition on several physiological and biochemical parameters of the green alga, Selenastrum minutum, have been examined. Algal cells were cultured in chemostats under conditions of either Pi limitation or nutrient sufficiency. Pi limitation resulted in: (a) a 5-fold lower rate of respiration, (b) a 3-fold decline in rates of photosynthetic carbon dioxide fixation and oxygen evolution, (c) a 3-fold higher rate of dark carbon dioxide fixation, (d) significant increases in activities of phosphoenolpyruvate (PEP) carboxylase and PEP phosphatase (128% and 158% of nutrient sufficient activities, respectively), (e) significant reductions in activities of nonphosphorylating NADP-glyceraldehyde-3-phosphate dehydrogenase and NAD malic enzyme, and (f) no change in levels of ATP:fructose-6-phosphate 1-phosphotransferase, phosphorylating NAD-glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase, and pyruvate kinase. The intracellular concentrations of Pi, ATP, AMP, soluble protein, and chlorophyll were also significantly reduced in response to Pi limitation. As well, the level of ADP was about 11-fold lower in the Pi-limited cells as compared to the nutrient sufficient controls. It was predicted that because of this low level of ADP, pyruvate kinase catalyzed conversion of PEP to pyruvate may be restricted in Pi-limited cells. During Pi limitation, PEP carboxylase and PEP phosphatase may function to "bypass" the ADP dependent pyruvate kinase, as well as to recycle Pi for its reassimilation into cellular metabolism.

Journal Article↗

Breast cancer in limited-resource countries: an overview of the Breast Health Global Initiative 2005 guidelines.

Breast cancer is the most common cause of cancer-related death among women worldwide, with case fatality rates highest in low-resource countries. Despite significant scientific advances in its management, most of the world faces resource constraints that limit the capacity to improve early detection, diagnosis, and treatment of the disease. The Breast Health Global Initiative (BHGI) strives to develop evidence-based, economically feasible, and culturally appropriate guidelines that can be used in nations with limited health care resources to improve breast cancer outcomes. Using an evidence-based consensus panel process, four BHGI expert panels addressed the areas of early detection and access to care, diagnosis and pathology, treatment and resource allocation, and health care systems and public policy as they relate to breast health care in limited-resource settings. To update and expand on the BHGI Guidelines published in 2003, the 2005 BHGI panels outlined a stepwise, systematic approach to health care improvement using a tiered system of resource allotment into four levels-basic, limited, enhanced, and maximal-based on the contribution of each resource toward improving clinical outcomes. Early breast cancer detection improves outcome in a cost-effective fashion assuming treatment is available, but requires public education to foster active patient participation in diagnosis and treatment. Clinical breast examination combined with diagnostic breast imaging (ultrasound +/- diagnostic mammography) can facilitate cost-effective tissue sampling techniques for cytologic or histologic diagnosis. Breast-conserving treatment with partial mastectomy and radiation therapy requires more health care resources and infrastructure than mastectomy, but can be provided in a thoughtfully designed limited-resource setting. The availability and administration of systemic therapies are critical to improving breast cancer survival. Estrogen receptor testing allows patient selection for hormonal treatments (tamoxifen, oophorectomy). Chemotherapy, which requires some allocation of resources and infrastructure, is needed to treat node-positive, locally advanced breast cancers, which represent the most common clinical presentation of disease in low-resource countries. When chemotherapy is not available, patients with locally advanced, hormone receptor-negative cancers can only receive palliative therapy. Future research is needed to better determine how these guidelines can best be implemented in limited-resource settings.

Breast Neoplasms↗

Breast cancer in limited-resource countries: diagnosis and pathology.

In 2002 the Breast Health Global Initiative (BHGI) convened a panel of breast cancer experts and patient advocates to develop consensus recommendations for diagnosing breast cancer in countries with limited resources. The panel agreed on the need for a pathologic diagnosis, based on microscopic evaluation of tissue specimens, before initiating breast cancer treatment. The panel discussed options for pathologic diagnosis (fine-needle aspiration biopsy, core needle biopsy, and surgical biopsy) and concluded that the choice among these methods should be based on available tools and expertise. Correlation of pathology, clinical, and imaging findings was emphasized. A 2005 BHGI panel reaffirmed these recommendations and additionally stratified diagnostic and pathology methods into four levels--basic, limited, enhanced, and maximal--from lowest to highest resources. The minimal requirements (basic level) include a history, clinical breast examination, tissue diagnosis, and medical record keeping. Fine-needle aspiration biopsy was recognized as the least expensive reliable method of tissue sampling, and the need for comparing its clinical usefulness with that of core needle biopsy in the limited-resource setting was emphasized. Increasing resources (limited level) may enable diagnostic breast imaging (ultrasound +/- mammography), use of tests to evaluate for metastases, limited image-guided sampling, and hormone receptor testing. With more resources (enhanced level), diagnostic mammography, bone scanning, and an onsite cytologist may be possible. Mass screening mammography is introduced at the maximal-resource level. At all levels, increasing breast cancer awareness, diagnosing breast cancer at an early stage, training individuals to perform and interpret breast biopsies, and collecting statistics about breast cancer, resources, and competing priorities may improve breast cancer outcomes in countries with limited resources. Expertise in pathology was reaffirmed to be a key requirement for ensuring reliable diagnostic findings. Several approaches were again proposed for improving breast pathology, including training pathologists, establishing pathology services in centralized facilities, and organizing international pathology services.

Biopsy, Needle↗

Breast cancer in limited-resource countries: treatment and allocation of resources.

Treating breast cancer under the constraints of significantly limited health care resources poses unique challenges that are not well addressed by existing guidelines. We present evidence-based guidelines for systematically prioritizing cancer therapies across the entire spectrum of resource levels. After consideration of factors affecting the value of a given breast cancer therapy (contribution to overall survival, disease-free survival, quality of life, and cost), we assigned each therapy to one of four incremental levels--basic, limited, enhanced, or maximal--that together map out a sequential and flexible approach for planning, establishing, and expanding breast cancer treatment services. For stage I disease, basic-level therapies are modified radical mastectomy and endocrine therapy with ovarian ablation or tamoxifen; therapies added at the limited level are breast-conserving therapy, radiation therapy, and standard-efficacy chemotherapy (cyclophosphamide, methotrexate, and 5-fluorouracil [CMF], or doxorubicin and cyclophosphamide [AC], epirubicin and cyclophosphamide [EC], or 5-fluorouracil, doxorubicin, and cyclophosphamide [FAC]); at the enhanced level, taxane chemotherapy and endocrine therapy with aromatase inhibitors or luteinizing hormone-releasing hormone (LH-RH) agonists; and at the maximal level, reconstructive surgery, dose-dense chemotherapy, and growth factors. For stage II disease, the therapy allocation is the same, with the exception that standard-efficacy chemotherapy is a basic-level therapy. For locally advanced breast cancer, basic-level therapies are modified radical mastectomy, neoadjuvant chemotherapy (CMF, AC, or FAC), and endocrine therapy with ovarian ablation or tamoxifen; the therapy added at the limited level is postmastectomy radiation therapy; at the enhanced level, breast-conserving therapy, breast-conserving whole-breast radiation therapy, taxane chemotherapy, and endocrine therapy with aromatase inhibitors or LH-RH agonists; and at the maximal level, reconstructive surgery and dose-dense chemotherapy and growth factors. For metastatic or recurrent disease, basic-level therapies are total mastectomy for ipsilateral in-breast recurrence, endocrine therapy with ovarian ablation or tamoxifen, and analgesics; therapies added at the limited level are radiation therapy and CMF or anthracycline chemotherapy; at the enhanced level, chemotherapy with taxanes, capecitabine, or trastuzumab, endocrine therapy with aromatase inhibitors, and bisphosphonates; and at the maximal level, chemotherapy with vinorelbine, gemcitabine, or carboplatin, growth factors, and endocrine therapy with fulvestrant. Compared with the treatment of early breast cancer, the treatment of advanced breast cancer is more resource intensive and generally has poorer outcomes, highlighting the potential benefit of earlier detection and diagnosis, both in terms of conserving scarce resources and in terms of reducing morbidity and mortality. Use of the scheme outlined here should help ministers of health, policymakers, administrators, and institutions in limited-resource settings plan, establish, and gradually expand breast cancer treatment services for their populations.

Aromatase Inhibitors↗

Phosphate limitation induces catalase expression in Sinorhizobium meliloti, Pseudomonas aeruginosa and Agrobacterium tumefaciens.

Growth of Sinorhizobium meliloti under Pi-limiting conditions induced expression of the major H2O2-inducible catalase (HPII) gene (katA) in this organism. This transcription required the PhoB transcriptional regulator and initiated from a promoter that was distinct from the OxyR-dependent promoter which activates katA transcription in response to addition of H2O2. In N2-fixing root nodules, katA was transcribed from the OxyR- and not the PhoB-dependent promoter. This is consistent with the accumulation of reactive oxygen species (ROS) in nodules and also indicates that bacteroids within nodules are not Pi-limited. Pi-limited growth also induced expression of catalase genes in Agrobacterium tumefaciens (HPI) and Pseudomonas aeruginosa (PA4236-HPI) suggesting that this may be a widespread phenomenon. The response is not a general stress response as in both S. meliloti and P. aeruginosa increased transcription is mediated by the phosphate responsive transcriptional activator PhoB. The phenotypic consequences of this response were demonstrated in S. meliloti by the dramatic increase in H2O2 resistance of wild type but not phoB mutant cells upon growth in Pi-limiting media. Our data indicate that in S. meliloti, katA and other genes whose products are involved in protection from oxidative stress are induced upon Pi-limitation. These observations suggest that as part of the response to Pi-limitation, S. meliloti, P. aeruginosa and A. tumefaciens have evolved a capacity to increase their resistance to oxidative stress. Whether this capacity evolved because Pi-starved cells generate more ROS or whether the physiological changes that occur in the cells in response to Pi-starvation render them more sensitive to ROS remains to be established.

Agrobacterium tumefaciens↗

Interactions between the YycFG and PhoPR two-component systems in Bacillus subtilis: the PhoR kinase phosphorylates the non-cognate YycF response regulator upon phosphate limitation.

Two-component signal transduction systems (TCS) are an important mechanism by which bacteria sense and respond to their environment. Although each two-component system appears to detect and respond to a specific signal(s), it is now evident that they do not always act independently of each other. In this paper we present data indicating regulatory links between the PhoPR two-component system that participates in the cellular response to phosphate limitation, and the essential YycFG two-component system in Bacillus subtilis. We show that the PhoR sensor kinase can activate the YycF response regulator during a phosphate limitation-induced stationary phase, and that this reaction occurs in the presence of the cognate YycG sensor kinase. Phosphorylation of YycF by PhoR also occurs in vitro, albeit at a reduced level. However, the reciprocal cross-phosphorylation does not occur. A second level of interaction between PhoPR and YycFG is indicated by the fact that cells depleted for YycFG have a severely deficient PhoPR-dependent phosphate limitation response and that YycF can bind directly to the promoter of the phoPR operon. YycFG-depleted cells neither activate expression of phoA and phoPR nor repress expression of the essential tagAB and tagDEF operons upon phosphate limitation. This effect is specific to the PhoPR-dependent phosphate limitation response because PhoPR-independent phosphate limitation responses can be initiated in YycFG-depleted cells.

Alkaline Phosphatase↗

The hydraulic limitation hypothesis revisited.

We proposed the hydraulic limitation hypothesis (HLH) as a mechanism to explain universal patterns in tree height, and tree and stand biomass growth: height growth slows down as trees grow taller, maximum height is lower for trees of the same species on resource-poor sites and annual wood production declines after canopy closure for even-aged forests. Our review of 51 studies that measured one or more of the components necessary for testing the hypothesis showed that taller trees differ physiologically from shorter, younger trees. Stomatal conductance to water vapour (g(s)), photosynthesis (A) and leaf-specific hydraulic conductance (K L) are often, but not always, lower in taller trees. Additionally, leaf mass per area is often greater in taller trees, and leaf area:sapwood area ratio changes with tree height. We conclude that hydraulic limitation of gas exchange with increasing tree size is common, but not universal. Where hydraulic limitations to A do occur, no evidence supports the original expectation that hydraulic limitation of carbon assimilation is sufficient to explain observed declines in wood production. Any limit to height or height growth does not appear to be related to the so-called age-related decline in wood production of forests after canopy closure. Future work on this problem should explicitly link leaf or canopy gas exchange with tree and stand growth, and consider a more fundamental assumption: whether tree biomass growth is limited by carbon availability.

Biomass↗

Factors associated with functional limitations and subsequent employment or schooling in Buruli ulcer patients.

OBJECTIVES: To evaluate former Buruli ulcer disease (BUD) patients to assess the factors associated with functional limitations and subsequent employment or schooling. METHODS: The previously validated Buruli ulcer functional limitation score (BUFLS) questionnaire and interviews about educational and professional consequences incurred by BUD. RESULTS: Of 638 participants, 362 (57%) had a functional limitation after a median period of almost 4 years after treatment for BUD. A lesion on a joint, older age, female gender, a lesion on a distal part of an extremity and a persistent wound were found to be independent risk factors for stopping work or education. The same risk factors applied to the development of a functional limitation. Both functional limitations and financial difficulties due to BUD disease often led to job loss and school dropout. CONCLUSIONS: Rehabilitation programmes are urgently needed to diminish the suffering from the functional limitations and employment or schooling problems caused by BUD.

Adolescent↗

Alteration of the intracellular concentration of aminoacyl-tRNA synthetases and isoaccepting tRNAs during amino-acid limited growth in Escherichia coli.

Growth of Escherichia coli AB 2271 under threonine or isoleucine deficiency leads to a depression of the threonyl-tRNA synthetase and isoleucyl-tRNA synthetase respectively. During this amino-acid-limited growth the concentrations of isoaccepting fractions of the cognate tRNA species were changed, as demonstrated by their altered reversed-phase-5 chromatograms. But, in addition, the profiles of the isoacceptors of all other tRNA species investigated, i.e. of tRNAsLeu, tRNAsSer and tRNAsArg were also altered. This means that, if there is a correlation between regulation of the level of an aminoacyl-tRNA synthetase and its cognate isoaccepting tRNAs, it is superimposed by the effect of amino acid limitation upon the concentration of all isoaccepting tRNAs. So far drastic changes in profiles of isoaccepting tRNAs have only been observed under unbalanced growth in relaxed cells or during treatment with antibiotics. Here we demonstrate that similar heavy alterations in patterns of isoaccepting tRNAs occur in a proven stringent E. coli strain growing exponentially under amino acid limitation. Thus the observed changes in the profiles of isoaccepting tRNAs during amino acid limitation signal a meaningful biological function of those newly or increasingly occurring isoaccepting tRNAs. During the growth under amino acid limitation the total acceptor activity of eight investigated tRNA species, however, stayed unchanged, except that under threonine-limited growth the total amount of tRNAIle was reduced to about half and that of tRNAGlu increased; both tRNA species of these isoacceptors are known [30,31] as spacers between ribosomal RNAs.

Amino Acids↗

Isolation and characterization of ubiquinol oxidase complexes from Paracoccus denitrificans cells cultured under various limiting growth conditions in the chemostat.

To obtain more information about the composition of the respiratory chain under different growth conditions and about the regulation of electron-transfer to several oxidases and reductases, ubiquinol oxidase complexes were partially purified from membranes of Paracoccus denitrificans cells grown in carbon-source-limited aerobic, nitrate-limited anaerobic and oxygen-limited chemostat cultures. The isolated enzymes consisted of cytochromes bc1, c552 and aa3. In comparison with the aerobic ubiquinol oxidase complex, the oxygen- and nitrate-limited ones contained, respectively, less and far less of the cytochrome aa3 subunits and the anaerobic complex also contained lower amounts of cytochrome c552. In addition, extra haem-containing polypeptides were present with apparent Mr of 14,000, 30,000 and 45,000, the former one only in the anaerobic and the latter two in both the anaerobic and oxygen-limited preparations. This is the first report describing four different membrane-bound c-type cytochromes. The potentiometric and spectral characteristics of the redox components in membrane particles and isolated ubiquinol oxidase fractions were determined by combined potentiometric analysis and spectrum deconvolution. Membranes of nitrate- and oxygen-limited cells contained extra high-potential cytochrome b in comparison with the membranes of aerobically grown cells. No difference was detected between the three isolated ubiquinol oxidase complexes. Aberrances with already published values of redox potentials are discussed.

Aerobiosis↗

Propagule vs. niche limitation: untangling the mechanisms behind plant species' distributions.

Distinguishing the roles of propagule limitation and niche requirements in controlling plant species distributions is important for understanding community structure, invasion, and restoration. We used species distribution models based on plant and environmental survey data to assess the strength of species' affinities for particular environmental conditions. We hypothesized that species with statistically detectable environmental requirements were primarily niche-limited, while species with weak habitat affinities were primarily propagule-limited. We tested this hypothesis via a seeding experiment in which we compared species' reproductive fitness in occupied and unoccupied sites. Species that appeared to be niche-limited based on distribution models had lower fitness when planted in unoccupied sites, while species that models suggested were propagule-limited had equivalent fitness when planted in occupied and unoccupied sites. Our results demonstrate that within a single community, both species limited primarily by niche availability or primarily by propagule availability can be identified using observational data.

Ecosystem↗

Brief report: screening items to identify patients with limited health literacy skills.

BACKGROUND: Patients with limited literacy skills are routinely encountered in clinical practice, but they are not always identified by clinicians. OBJECTIVE: To evaluate 3 candidate questions to determine their accuracy in identifying patients with limited or marginal health literacy skills. METHODS: We studied 305 English-speaking adults attending a university-based primary care clinic. Demographic items, health literacy screening questions, and the Rapid Estimate of Adult Literacy in Medicine (REALM) were administered to patients. To determine the accuracy of the candidate questions for identifying limited or marginal health literacy skills, we plotted area under the receiver operating characteristic (AUROC) curves for each item, using REALM scores as a reference standard. RESULTS: The mean age of subjects was 49.5; 67.5% were female, 85.2% Caucasian, and 81.3% insured by TennCare and/or Medicare. Fifty-four (17.7%) had limited and 52 (17.0%) had marginal health literacy skills. One screening question, "How confident are you filling out medical forms by yourself?" was accurate in detecting limited (AUROC of 0.82; 95% confidence interval [CI]=0.77 to 0.86) and limited/marginal (AUROC of 0.79; 95% CI=0.74 to 0.83) health literacy skills. This question had significantly greater AUROC than either of the other questions (P<.01) and also a greater AUROC than questions based on demographic characteristics. CONCLUSIONS: One screening question may be sufficient for detecting limited and marginal health literacy skills in clinic populations.

Adolescent↗

Type and intensity of activity and risk of mobility limitation: the mediating role of muscle parameters.

OBJECTIVES: To investigate the association between different types of physical activity behavior and incident mobility limitation in older men and women and to examine whether muscle parameters mediate these associations. DESIGN: Cohort study with 4.5-year follow-up. SETTING: Metropolitan areas surrounding Pittsburgh, Pennsylvania, and Memphis, Tennessee. A random sample of white Medicare beneficiaries and all age-eligible blacks. PARTICIPANTS: Three thousand seventy-five black and white men and women aged 70 to 79 with no self-reported difficulty walking one-quarter of a mile or climbing 10 steps, enrolled in the Health, Aging and Body Composition (Health ABC) Study. MEASUREMENTS: Participants were classified as exercisers (reporting > or = 1,000 kcal/wk of exercise activity), lifestyle active (reporting < 1,000 kcal/wk of exercise activity and > or = 2,719 kcal/wk of total physical activity), or inactive (reporting < 1,000 kcal/wk of exercise activity and < 2,719 kcal/wk of total physical activity). The study outcome, incident mobility limitation, was defined as two consecutive, semiannual self-reports of any difficulty walking one quarter of a mile or climbing 10 steps. Thigh muscle area, thigh muscle attenuation (a marker of fat infiltration in muscle), appendicular lean soft tissue mass, and isokinetic knee extensor strength were examined as potential mediators. RESULTS: Over 4.5 years, 34.3% of men and 47.4% of women developed mobility limitation. Inactive persons had twice the risk of incident mobility limitation as exercisers (hazard ratio (HR)=2.08, 95% confidence interval (CI)=1.60-2.70, for men, HR=1.98, 95% CI=1.51-2.60, for women). Lifestyle-active men and women had an intermediate risk (HR=1.47 and 1.44, respectively). For the lifestyle active and inactive, absence of walking activity conferred an additional risk of mobility limitation. Muscle parameters did not mediate the relationship between physical activity and mobility limitation, except for knee extensor strength in men. CONCLUSION: Exercise and an active lifestyle that includes walking protect against mobility loss in older men and women. Activity effects on muscle parameters do not explain this association.

Activities of Daily Living↗

Longitudinal growth analysis of horses following limited and ad libitum feeding.

Eighteen colts were assigned to one of two groups: limit or ad libitum feeding. Three periods were evaluated: 1) six to 12 months, 2) 12 to 18 months and 3) 18 to 24 months of age. At 24 months of age, ad libitum fed horses weighed 13 per cent (51 kg) more and were 3.6 per cent (5.2 cm) taller than those fed limited amounts. Total, fore and hind body mass increased quadratically irrespective of dietary treatment. Fore body mass comprised 57 per cent of total body mass for both groups and this did not change with age or dietary treatment. Heart girth was directly related (R2 = 0.96) to total body mass. Average daily gains in total body mass of ad libitum fed horses were 13 and 71 per cent more rapid (P less than 0.05) than for limit fed horses in Periods 1 and 3, respectively. Ad libitum fed horses gained hind body mass 25 per cent more rapidly (P less than 0.05) than limit fed horses only in Period 1. Growth curves of wither and croup heights were quadratic in form. Ad libitum fed horses gained 12 and 13 per cent more rapidly at the wither than limit fed horses in Period 1 and overall, respectively. Ad libitum fed horses grew 33 per cent more rapidly at the croup than limit fed horses but only in Period 2. From six to 12 months of age, the wither and croup grew two-fold and four-fold more rapidly than between 12 to 18 months and between 18 to 24 months of age, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗

The lower limit of pitch as determined by rate discrimination.

This paper is concerned with the lower limit of pitch for complex, harmonic sounds, like the notes produced by low-pitched musical instruments. The lower limit of pitch is investigated by measuring rate discrimination thresholds for harmonic tones filtered into 1.2-kHz-wide bands with a lower cutoff frequency, F(c), ranging from 0.2 to 6.4 kHz. When F(c) is below 1 kHz and the harmonics are in cosine phase, rate discrimination threshold exhibits a rapid, tenfold decrease as the repetition rate is increased from 16 to 64 Hz, and over this range, the perceptual quality of the stimuli changes from flutter to pitch. When F(c) is increased above 1 kHz, the slope of the transition from high to low thresholds becomes shallower and occurs at progressively higher rates. A quantitative comparison of the cosine-phase thresholds with subjective estimates of the existence region of pitch from the literature shows that the transition in rate discrimination occurs at approximately the same rate as the lower limit of pitch. The rate discrimination experiment was then repeated with alternating-phase harmonic tones whose envelopes repeat at twice the repetition rate of the waveform. In this case, when F(c) is below 1 kHz, the transition in rate discrimination is shifted downward by almost an octave relative to the transition in the cosine-phase thresholds. The results support the hypothesis that in the low-frequency region, the pitch limit is determined by a temporal mechanism, which analyzes time intervals between peaks in the neural activity pattern. It seems that temporal processing of pitch is limited to time intervals less than 33 ms, corresponding to a pitch limit of about 30 Hz.

Adult↗