Hysteresis phenomenon in turbulent convection

Coherent large-scale circulations of turbulent thermal convection in air have been studied experimentally in a rectangular box heated from below and cooled from above using Particle Image Velocimetry. The hysteresis phenomenon in turbulent convection was found by varying the temperature difference between the bottom and the top walls of the chamber (the Rayleigh number was changed within the range of $10^7 - 10^8$). The hysteresis loop comprises the one-cell and two-cells flow patterns while the aspect ratio is kept constant ($A=2 - 2.23$). We found that the change of the sign of the degree of the anisotropy of turbulence was accompanied by the change of the flow pattern. The developed theory of coherent structures in turbulent convection (Elperin et al. 2002; 2005) is in agreement with the experimental observations. The observed coherent structures are superimposed on a small-scale turbulent convection. The redistribution of the turbulent heat flux plays a crucial role in the formation of coherent large-scale circulations in turbulent convection.Comment: 10 pages, 9 figures, REVTEX4, Experiments in Fluids, 2006, in pres

Mean flow instabilities of two-dimensional convection in strong magnetic fields

The interaction of magnetic fields with convection is of great importance in astrophysics. Two well-known aspects of the interaction are the tendency of convection cells to become narrow in the perpendicular direction when the imposed field is strong, and the occurrence of streaming instabilities involving horizontal shears. Previous studies have found that the latter instability mechanism operates only when the cells are narrow, and so we investigate the occurrence of the streaming instability for large imposed fields, when the cells are naturally narrow near onset. The basic cellular solution can be treated in the asymptotic limit as a nonlinear eigenvalue problem. In the limit of large imposed field, the instability occurs for asymptotically small Prandtl number. The determination of the stability boundary turns out to be surprisingly complicated. At leading order, the linear stability problem is the linearisation of the same nonlinear eigenvalue problem, and as a result, it is necessary to go to higher order to obtain a stability criterion. We establish that the flow can only be unstable to a horizontal mean flow if the Prandtl number is smaller than order , where B0 is the imposed magnetic field, and that the mean flow is concentrated in a horizontal jet of width in the middle of the layer. The result applies to stress-free or no-slip boundary conditions at the top and bottom of the layer

Discrete Wavelet Transform-Partial Least Squares Versus Derivative Ratio Spectrophotometry for Simultaneous Determination of Chlorpheniramine Maleate and Dexamethasone in the Presence of Parabens in Pharmaceutical Dosage Form

Purpose: To compare two methods, based on different approaches, for simultaneous determination of chlorpheniramine maleate (CHP) and dexamethasone (DX) in the presence of methyl and propyl paraben in phenadone syrup.Methods: The first method used, based on univariate calibration approach, was first derivative of the ratio spectrophotometry (DD1). The second method, which  is a multivariate calibration approach, was discrete wavelet transform followed by partial least squares method (DWT-PLS) which anticipated high predictive ability for the determination of both CHP and DX.Results: DD1 method failed to determine DX due to the absence of adequate zero crossing point while DWT-PLS method was successfully applied for the analysis of raw materials and the dosage form. For DD1 method, recovery of chlorpheniramine maleate in the dosage form was 100.33 ± 0.91 % while for DWT-PLS method, recovery of chlorpheniramine maleate and dexamethasone was 100.24 ± 1.21 and 99.99 ± 1.08 %, respectively. The proposed methods were validated using  standard addition technique and the results compared favorably with those obtained by a reference high performance liquid chromatography (HPLC) method.Conclusion: The findings of this work show the superiority of DWT-PLS over DD1 method in solving such complex mixtures, and would thus be suitable for use in quality control (QC) laboratories and pharmaceutical industry.Keywords: Quantitative analysis, Discrete wavelet transform, First derivative of ratio spectra, Chlorpheniramine maleate, Dexamethason

Novel Ratio Subtraction and Isoabsorptive Point Methods for Determination of Ambroxol Hydrochloride and Doxycycline in their Combined Dosage Form: Development and Validation

Purpose: To develop and validate two innovative spectrophotometric methods used for the simultaneous determination of ambroxol hydrochloride and doxycycline in their binary mixture.Methods: Ratio subtraction and isoabsorptive point methods were used for the simultaneous determination of ambroxol hydrochloride and doxycycline in their binary mixture. Linear correlations were obtained in the concentration range of 6 - 40 and 4 - 32 μg mL-1 for ambroxol hydrochloride and doxycycline, respectively. Ratio subtraction method was utilized for determination of ambroxol hydrochloride at 246.5 nm while isoabsorptive point method was employed for doxycycline at 244 nm (using methanol as a solvent) in mixtures as well as in their combined dosage form (Ambrodoxy capsules).Results: The proposed methods were successfully applied to the analysis of the pharmaceutical capsules containing the two analytes. Recovery for ambroxol hydrochloride and doxycycline in capsules was 99.49 and 99.96 %, respectively. The relative standard deviation (% RSD) for the assay of the capsules was < 1 %. Validation of the two methods was assessed according to International Council on Harmonization (ICH) guidelines regarding linearity, accuracy, precision, specificity and range. The results of the proposed methods compared favorably with those obtained by a reported chemometricsassisted ultraviolet (UV)-spectroscopic method.Conclusion: The proposed methods are rapid, selective, simple and accurate. They also represent suitable alternatives to the chromatographic methods currently used for the analysis of the pharmaceutical mixtures in various dosage forms.Keywords: Ambroxol, Doxycycline, Ratio subtraction method, Isoabsorptive point method, Binary mixture, Spectrophotometr

The Underestimation Of Egocentric Distance: Evidence From Frontal Matching Tasks

There is controversy over the existence, nature, and cause of error in egocentric distance judgments. One proposal is that the systematic biases often found in explicit judgments of egocentric distance along the ground may be related to recently observed biases in the perceived declination of gaze (Durgin & Li, Attention, Perception, & Psychophysics, in press), To measure perceived egocentric distance nonverbally, observers in a field were asked to position themselves so that their distance from one of two experimenters was equal to the frontal distance between the experimenters. Observers placed themselves too far away, consistent with egocentric distance underestimation. A similar experiment was conducted with vertical frontal extents. Both experiments were replicated in panoramic virtual reality. Perceived egocentric distance was quantitatively consistent with angular bias in perceived gaze declination (1.5 gain). Finally, an exocentric distance-matching task was contrasted with a variant of the egocentric matching task. The egocentric matching data approximate a constant compression of perceived egocentric distance with a power function exponent of nearly 1; exocentric matches had an exponent of about 0.67. The divergent pattern between egocentric and exocentric matches suggests that they depend on different visual cues

Prevalence of the metabolic syndrome among patients with type 2 diabetes mellitus in urban North-Central Nigeria.

Background: In most people with glucose intolerance or type 2 diabetes mellitus (DM), there is a multiple set of risk factors that commonly appear together forming what is now known as the ‘Metabolic Syndrome’ (MS). This ‘clustering’ of metabolic abnormalities that occur in the same individual appear to confer substantial additional cardiovascular risk. There has been no report on the MS among patients with type 2 DM in urban North-central Nigeria. Objective: The objective of this study was to determine the prevalence of the MS among urban North-central Nigerians with type 2 DM and to describe the frequency of the syndrome’s components. Methods: Six hundred and thirty four (634) patients with type 2 diabetes attending the out-patient clinic of the Diabetes Screening and Care Centre, Jos, Nigeria were screened for the MS. A brief history was obtained and their anthropometric indices and blood pressure were measured. Fasting venous plasma samples were analyzed for lipids. Early morning spot urine samples were obtained for estimation of microalbuminuria using the Bayer DCA 2000® machine. The diagnosis of MS was made based on the new International Diabetes Federation (IDF) definition. Results: Of the 634 patients enrolled with mean (standard deviation/SD) age 54.2(9.1) years, 56% were females. The prevalence of MS was 63.6% (74.5% in males and 54.9% in females,

PROGNOSTIC TEST OF SOFA SCORE WITH THE ADDITION OF LACTATE LEVELS IN PREDICTING 28-DAY MORTALITY OF SEPSIS PATIENTS IN THE INTENSIVE CARE UNIT AT RSMH PALEMBANG

Sepsis is defined as a life-threatening organ dysfunction caused by the host's unresolved response to infection. Many scoring or biomarkers can be used as a prognostic scoring scoring. Lactate is an indirect measurement of tissue perfusion. SOFA scores and can be applied in predicting independent mortality. Also recently found an increase in SOFA along with an increase in lactate. This study aims to determine the ability of SOFA scores with addition of lactate in predicting mortality in sespsis patients. Observational analytic study with a cross- sectional design using data of sepsis patients treated from January - December 2018 at RSMH Palembang. Inclusion criteria in this study were patients who were treated in intensive care with a diagnosis of sepsis and aged > 18 years with exclusion criteria had incomplete medical record data, referral patients from other hospitals, patients treated less than 24 hours in RSMH Palembang and readmission patients to the intensive unit in the same maintenance period. SOFA scores with additional Lactate levels had a cut-off point of ? 12 with a sensitivity value of 85.0%, specificity: 85.4%, AUC: 92.8%, while the SOFA score had a cut-off point of ?7 with a sensitivity value of 80%, Specificity: 72.9%, AUC: 81.1% in predicting the 28-day mortality of sepsis patients at RSMH Palembang. There was a difference in the prognostic value of the SOFA score with the addition of lactate levels compared to the SOFA score in predicting 28-day mortality of sepsis patients in the intensive care unit of RSMH Palembang

Isozyme and allozyme markers distinguishing two morphologically similar, medically important Mastomys species (Rodentia: Muridae)

BACKGROUND: Two common southern African mice species, Mastomys coucha and M. natalensis, are widely distributed throughout the subregion and overlap in many areas. They also share a high degree of morphological similarity, making them impossible to distinguish in the field at present. These multimammate mice are documented carriers of serious disease vectors causing Lassa fever, plague and encephalomyocarditis, which coupled to their cohabitation with humans in many areas, could pose a significant health risk. A preliminary study reported the presence of isozyme markers at three loci (GPI-2, PT-2, -3) in one population each of M. coucha and M. natalensis. Two additional populations (from the Vaal Dam and Richards Bay) were sampled to determine the reliability of these markers, and to seek additional genetic markers. RESULTS: Fifteen proteins or enzymes provided interpretable results at a total of 39 loci. Additional fixed allele differences between the species were detected at AAT-1, ADH, EST-1, PGD-1, Hb-1 and -2. Average heterozygosities for M. coucha and M. natalensis were calculated as 0.018 and 0.032 respectively, with a mean genetic distance between the species of 0.26. CONCLUSIONS: The confirmation of the isozyme and the detection of the additional allozyme markers are important contributions to the identification of these two medical and agricultural pest species