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At least 235 records · Page 13Linked to original sources
PubMed2004

[Severe Class III malocclusion: long-term stability. Retrospective analysis of 12 cases].

PURPOSE: Long-term stability of severe class III is rarely evaluated in the literature. We present our findings with 12 patients who underwent surgery from June 1995 to December 1997 and analyze cephalometric superpositions. MATERIALS AND METHODS: Twelve operated patients were reviewed to analyze long-term results (follow-up 3 years 8 months). The sex ratio was well balanced. Mean age was 23 years. All patients were given pre- and postoperative orthodontic care and underwent bimaxillary surgery with Lefort 1 osteotomy and sagittal osteotomy of the rami. Delaire cephalometry on preoperative and early and late postoperative films was used to analyze outcome. Skeletal instability was defined as displacement greater than 4 mm. Recurrence was defined as secondary loss of the functional and esthetic result. RESULTS: Four patients (33%) developed skeletal instability. All patients achieved long-term stability. DISCUSSION: To detail the cause of skeletal instability, study of the principal factors of instability is presented together with a discussion of data in the literature.

Adolescent↗
PubMed2003

The mammalian XRCC genes: their roles in DNA repair and genetic stability.

Analysis of the XRCC genes has played an important part in understanding mammalian DNA repair processes, especially those involved in double-strand break (DSB) repair. Most of these genes were identified through their ability to correct DNA damage hypersensitivity in rodent cell lines, and they represent components of several different repair pathways including base-excision repair, non-homologous end joining, and homologous recombination. We document the phenotypic effects of mutation of the XRCC genes, and the current state of our knowledge of their functions. In addition to their continuing importance in discovering mechanisms of DNA repair, analysis of the XRCC genes is making a substantial contribution to the understanding of specific human disorders, including cancer.

Animals↗
PubMed1999

Virus-inducible expression of a host chemokine gene relies on replication-linked mRNA stabilization.

Analysis of the host response to viral infection generally has focused on the capacity of viruses to activate or repress transcription of cellular genes, and this approach is also characteristic of work on RNA viruses such as respiratory syncytial virus (RSV). In the present study, it appeared initially that RSV-driven expression of a critical immune regulator, the beta-chemokine RANTES (regulated upon activation, normal T cell expressed and secreted), in primary-culture airway epithelial cells also depended on inducible gene transcription because expression was accompanied by coordinate increases in transcriptional initiation rate and gene promoter activity. However, RSV-driven increases in RANTES gene transcription and promoter activity were small and transient relative to RANTES expression, and they were no different in size and duration than for inactivated RSV that was incapable of fully inducing RANTES expression. These findings suggested that the increase in RANTES gene transcription was not sufficient for inducible expression and that critical regulatory effects occurred at a posttranscriptional level. This type of mechanism for virus-inducible expression of RANTES was established when we found that replicating (but not inactivated) RSV markedly increased RANTES mRNA half-life (from 0.8 to 6.8 h). In addition, RNase protection assays of heterologous promoter/reporter plasmids indicate that basal instability of RANTES mRNA is mediated at least in part by nucleotides 11-389 of the RANTES gene, and this region is also the target for induction by virus. The distinct pathway for production of RANTES (in combination with cytokine-dependent expression of RANTES and related immune-response genes) may more effectively coordinate immune cell interaction with epithelial barrier cells to mediate host defense.

Bronchi↗
PubMed2006

Improved biplex quantitative real-time polymerase chain reaction with modified primers for gene expression analysis.

Stabilizing modified bases incorporated in primers allows the reduction of housekeeping gene primer concentration not possible with regular primers without sacrificing amplification efficiency. Low primer concentration allows coamplification of the most abundant housekeeping genes with very rare templates without mutual inhibition. Real-time polymerase chain reaction (PCR) coamplification of 18S ribosomal RNA with several genes of interest was used in this study with MGB Eclipse (Nanogen, San Diego, CA) hybridization probes. The results may be useful for high throughput gene expression studies as they simplify validation experiments.

Animals↗
PubMed2004

Dynamics and stability of vortex-antivortex fronts in type-II superconductors.

The dynamics of vortices in type-II superconductors exhibit a variety of patterns whose origin is poorly understood. This is partly due to the nonlinearity of the vortex mobility, which gives rise to singular behavior in the vortex densities. Such singular behavior complicates the application of standard linear stability analysis. In this paper, as a first step towards dealing with these dynamical phenomena, we analyze the dynamical stability of a front between vortices and antivortices. In particular, we focus on the question of whether an instability of the vortex front can occur in the absence of a coupling to the temperature. Borrowing ideas developed for singular bacterial growth fronts, we perform an explicit linear stability analysis which shows that, for sufficiently large front velocities and in the absence of coupling to the temperature, such vortex fronts are stable even in the presence of in-plane anisotropy. This result differs from previous conclusions drawn on the basis of approximate calculations for stationary fronts. As our method extends to more complicated models, which could include coupling to the temperature or to other fields, it provides the basis for a more systematic stability analysis of nonlinear vortex front dynamics.

Journal Article↗
PubMed2002

Sensitivity analysis of stabilization pond system design parameters.

Two stabilization pond systems are examined. A sensitivity analysis is undertaken, aimed at investigating the influence of the pond depths on stabilization pond surface area and pond volume for the specific combination of temperature, wastewater characteristics and effluent requirements. The dependencies are presented in a functional form, allowing for the graphical solution of the unit pond volume, area, and hydraulic residence time as a function of the respective pond depths. Based on these graphs, designers can determine the most appropriate depth value for each type of pond that minimizes the required area or volume, or balances excavation versus land acquisition and floor lining costs, taking under consideration the topographic and other local characteristics of the site area.

Costs and Cost Analysis↗
PubMed2003

ANCOVA approach for shelf life analysis of stability study of multiple factor designs.

For a traditional multiple batch stability design with no other factor, the conventional analysis is analysis of covariance (ANCOVA) modeling using F-tests based on type I sum of squares to determine whether the batches may be pooled for a common estimate of the linear regression line(s). In the last decade, many multiple factor designs were proposed in stability studies. With the objective of model selection, the generalization of the conventional ANCOVA model using type I sum of squares to designs with multiple factors requires a prespecified hierarchical pooling test ordering to determine whether any of the factors may be eliminated. Different shelf life estimates may be derived using different hierarchical pooling test orderings. On the other hand, setting the hierarchical ordering can be subjective and controversial. The stepwise modeling based on F-tests using type III sum of squares for model determination and factor elimination is proposed to eliminate such difficulties.

Drug Stability↗
PubMed2003

Direct measurement of multiple instability regions via a Fourier filtering method in an optical pattern forming system.

We determine the limits of stability of the homogeneous state of a pattern forming optical system in dependency on the wave number by experimental means. The measurement becomes feasible by adopting a scheme based on a Fourier filtering technique. The system under study is a single-mirror feedback arrangement using sodium vapor as the nonlinear medium. The experiment confirms the existence of multiple instability regions of the homogeneous state expected by theory. The measurements do not agree quantitatively with the marginal stability curve determined by a linear stability analysis of an infinitely extended homogeneous system. We study the system numerically and demonstrate that the results of the simulations for the case of a Gaussian beam can be reproduced by a simple modification of the linear stability analysis which accounts for the finite diameter of the input beam. This explains the wave number dependent systematic deviations between the experiment and the linear stability analysis of the infinitely extended system.

Journal Article↗
PubMed2006

Instability and dynamics of thin viscoelastic liquid films.

The instability, rupture, and subsequent growth of holes in a thin Jeffreys-type viscoelastic film under the influence of long-range van der Waals force are investigated using both linear stability analysis and nonlinear numerical solutions. The linear stability analysis of full governing equations valid for arbitrary wave numbers shows that although fluid rheology does not influence the dominant length scale of the instability, it significantly affects the growth rate. It is shown that neglect of inertia and solvent dynamics results in a nonphysical singularity in the growth rate beyond a critical value of relaxation time. We further carry out numerical simulations of a set of long-wave, nonlinear differential equations (also derived in Rauscher et al., Eur. Phys. J. E 17, 373 (2005)) governing the evolution of the free surface. The nonlinear simulations, in their domain of validity, confirm the results of the linear analysis. Interestingly, results from nonlinear simulations further show that both for Newtonian and viscoelastic liquids, the shape and the dewetting dynamics of a hole are identical when examined in terms of a rescaled time which depends on rheological parameters. Thus, viscoelasticity of Jeffreys type merely accelerates the growth rate, without however affecting the important morphological characteristics.

Computer Simulation↗
PubMed1986

Simultaneous high-performance liquid chromatographic stability-indicating analysis of acetaminophen, codeine phosphate, and sodium benzoate in elixirs.

A stability-indicating high-performance liquid chromatographic method has been developed for the simultaneous determination of acetaminophen, codeine phosphate and sodium benzoate in an elixir formulation. The reversed-phase paired-ion method utilizes UV detection at 214 nm, a C18 column at 50 degrees C and requires ca. 10 min per analysis. The method has been validated for use with elixirs containing 120 mg of acetaminophen, 12 mg of codeine phosphate and 7.5 mg sodium benzoate preservative per 5 ml. The known potential degradation products p-aminophenol, codeine N-oxide and codeinone are separated for quantitation simultaneous with the parent compounds. The method has been shown to be linear, reproducible, specific, sensitive and rugged.

Acetaminophen↗
PubMed2005

A meta-analysis of stability after anterior cruciate ligament reconstruction as a function of hamstring versus patellar tendon graft and fixation type.

PURPOSE: Four-strand hamstring graft (4HS) is stronger than 10-mm bone-patellar tendon-bone graft (BPTB) and has equal tunnel pullout strength, but is believed by some to produce lower rates of stability after anterior cruciate ligament reconstruction (ACLR). Our purpose was to test the hypothesis that 4HS ACLR with modern fixation would produce equal or greater stability than BPTB ACLR. TYPE OF STUDY: Meta-analysis. METHODS: A computer search was used to find all published reports of ACLR series using HS and/or BPTB. Inclusion criteria were minimum 24-month follow-up, stratified presentation of arthrometric stability data, and at least 30-lb arthrometric testing force. Twenty-four 4HS, 8 2-strand hamstring (2HS), and 32 BPTB series met these criteria and were subdivided into groups according to fixation type. We used the International Knee Documentation Committee classification of a side-to-side instrumented Lachman test difference of < or = 2 mm as normal stability, and > 5 mm difference as abnormal stability. Series with at least 80% normal and at most 3% abnormal stability were designated as high-stability. Meta-analytic methods were used to determine group level differences. RESULTS: Total 4HS had a higher normal stability rate than total BPTB: 77% versus 66%, P < .001; and lower abnormal stability: 4.4% versus 5.9%, P = .029. The 4HS ACLR using the EndoButton (Smith & Nephew Endoscopy, Andover, MA) and second-generation tibial fixation (EB2-4HS) had higher normal stability (80%) and lower abnormal stability (1.7%) than all other subgroups, including BPTB with 2 interference screws (70% normal, 5.0% abnormal) P < .001; 84% of the series in the EB2-4HS group were high-stability series. No more than 33% of the series from any other group were high-stability. CONCLUSIONS: The recent literature would suggest that 4HS ACLR produces higher stability rates than BPTB, that 4HS stability rates are fixation dependent, that aperture fixation offers no stability advantage, and that EndoButton with second-generation tibial fixation produces consistently high stability rates. LEVEL OF EVIDENCE: Level IV.

Anterior Cruciate Ligament↗
PubMed2000

Effect of incompressibility on lateral instabilities of polymer brushes in a poor solvent.

We report a theoretical investigation of the lateral instability of grafted polymer layers in a poor solvent. Within self-consistent mean-field theory, we carry out a linear stability analysis at the random phase approximation level, for which an explicit incompressibility condition is enforced. Our analysis predicts a stability diagram in which regions of stable and unstable polymer brush profiles are located. Compared with analysis where incompressibility is not taken into account, our results suggest that lateral stability is enhanced.

Journal Article↗
PubMed1998

Stability-indicating analysis of isoxazolyl penicillins using dual wavelength high-performance liquid chromatography.

Stability-indicating high-performance liquid chromatography analytical procedures were developed for specific determination of four isoxazolyl penicillins during degradation under neutral and accelerated acid/alkali conditions. The chromatographic conditions were set so that the drug peak was well separated from the peaks of the degradation products. Peak homogeneity of the resolving drug peak was assessed by the shape of the ratio chromatogram. Good and reproducible separations were achieved on a reversed-phase column using a mobile phase consisting of acetonitrile and a solution of 20 mM potassium dihydrogen phosphate plus 10 mM tetramethylammonium chloride in water (adjusted to pH 5). Optimal separations for all four drugs were achieved within the range of 15-21% organic modifier in the mobile phase. The detection wavelengths were 220 nm and 240 nm. The stability-indicating nature of the methods was confirmed by the linearity of the pseudo-first order plots. The utility of dual-wavelength chromatography in establishment of stability-indicating assays is highlighted.

Chromatography, High Pressure Liquid↗
PubMed2004

Evaluation of common organic solvents for gas chromatographic analysis and stability of multiclass pesticide residues.

In this study, we evaluated the suitability of six common organic solvents for gas chromatographic (GC) analysis of pesticides. Three of these, acetone, acetonitrile (MeCN) and ethyl acetate (EtAc), represent extraction solvents commonly used in multiresidue methods for determination of pesticides in produce. The other three, isooctane, hexane and toluene, often serve as exchange solvents before a GC analysis. An ideal solvent for GC analysis of multiclass pesticide residues should be compatible with: the analytes, sample preparation, and GC analysis. This study addresses each aspect with emphasis placed on stability of selected pesticides in the given solvents. In this respect, the exchange solvents proved to be superior to the more polar extraction solvents. Degradation of N-trihalomethylthio fungicides (e.g., captan, folpet, dichlofluanid) in MeCN was observed only in certain lots of the tested MeCN, but even if it occurred, the stability of these analytes as well as that of dicofol and chlorothalonil was dramatically improved by the addition of 0.1% (v/v) acetic acid. Dicofol and chlorothalonil were also unstable in acetone, and pesticides with a thioether group (e.g., fenthion, disulfoton) degraded in the tested EtAc. Formation of isomers of certain pyrethroids (deltamethrin, lambda-cyhalothrin) was recorded in the chromatograms from MeCN and acetone solutions, but this effect more likely occurred during the GC injection than in solution. For several reasons, MeCN was found to be the most suitable solvent for extraction of a wide polarity range of pesticide residues from produce. After acidification, the stability of problematic pesticides in MeCN is acceptable, and MeCN can also serve as a medium for GC injection; therefore solvent exchange is generally not required before GC analysis. If sensitivity is an issue in splitless injection, then toluene was demonstrated to be the best exchange solvent due to its miscibility with MeCN and stronger responses of relatively more polar pesticides (e.g., acephate, methamidophos) as compared to hexane and isooctane.

Organic Chemicals↗
PubMed1997

2'-Fluoro modified nucleic acids: polymerase-directed synthesis, properties and stability to analysis by matrix-assisted laser desorption/ionization mass spectrometry.

Fragmentation is a major factor limiting mass range and resolution in the analysis of DNA by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Protonation of the nucleobase leads to base loss and backbone cleavage by a mechanism similar to the depurination reactions employed in the chemical degradation method of DNA sequencing. In a previous study [Tang,W., Zhu,L. and Smith,L.M. (1997) Anal. Chem ., 69, 302-312], the stabilizing effect of substituting the 24 hydrogen with an electronegative group such as hydroxyl or fluorine was investigated. These 24 substitutions stabilized the N-glycosidic linkage, blocking base loss and subsequent backbone cleavage. For such chemical modifications to be of practical significance, it would be useful to be able to employ the corresponding 24-modified nucleoside triphosphates in the polymerase-directed synthesis of DNA. This would provide an avenue to the preparation of 24-modified PCR fragments and dideoxy sequencing ladders stabilized for MALDI analysis. In this paper methods are described for the polymerase-directed synthesis of 24-fluoro modified DNA, using commercially available 24-fluoronucleoside triphosphates. The ability of a number of DNA and RNA polymerases to incorporate the 24-fluoro analogs was tested. Four thermostable DNA polymerases [Pfu (exo-), Vent (exo-), Deep Vent (exo-) and UlTma] were found that were able to incorporate 24-fluoronucleotides with reasonable efficiency. In order to perform Sanger sequencing reactions, the enzymes' ability to incorporate dideoxy terminators in conjunction with the 24-fluoronucleotides was evaluated. UlTma DNA polymerase was found to be the best of the enzymes tested for this purpose. MALDI analysis of enzymatically produced 24-fluoro modified DNA using the matrix 2,5-dihydroxy benzoic acid showed no base loss or backbone fragmentation, in contrast to the extensive fragmentation evident with unmodified DNA of the same sequence.

DNA↗
PubMed1982

[Analysis and stability of atropine sulfate and scopolamine hydrobromide. 1. Qualitative detection of alkaloids in the presence of their decomposition products. 73. Contribution to the problem of the use of plastic receptacles for liquid pharmaceuticals].

The authors deal with the qualitative determination of tropane alkaloid salts (atropine sulphate and scopolamine hydrobromide) in aqueous solutions in the presence of their decomposition products using thin-layer chromatography. Aqueous solutions of these tropane alkaloid salts were tested for stability after storage in glass and polyethylene containers under various conditions (pH value, temperature, ultra-violet irradiation, oxidative effects). Besides tropine, apoatropine, alpha- and beta-belladonine, further decomposition products showing a basic reaction (and in part not yet identified) were detected. The stability of solid atropine sulphate was studied by means of differential thermal analysis and mass spectrometry.

Atropine↗
PubMed2003

Fast and accurate coarsening simulation with an unconditionally stable time step.

We present Cahn-Hilliard and Allen-Cahn numerical integration algorithms that are unconditionally stable and so provide significantly faster accuracy-controlled simulation. Our stability analysis is based on Eyre's theorem and unconditional von Neumann stability analysis, both of which we present. Numerical tests confirm the accuracy of the von Neumann approach, which is straightforward and should be widely applicable in phase-field modeling. For the Cahn-Hilliard case, we show that accuracy can be controlled with an unbounded time step Delta t that grows with time t as Delta t approximately t(alpha). We develop a classification scheme for the step exponent alpha and demonstrate that a class of simple linear algorithms gives alpha=1/3. For this class the speedup relative to a fixed time step grows with N, the linear size of the system, as N/ln N. With conservative choices for the parameters controlling accuracy and finite-size effects we find that an 8192(2) lattice can be integrated 300 times faster than with the Euler method.

Journal Article↗
PubMed1999

Chaotic jam and phase transition in traffic flow with passing.

The lattice hydrodynamic model is presented to take into account the passing effect in one-dimensional traffic flow. When the passing constant gamma is small, the conventional jamming transition occurs between the uniform traffic and kink density wave flows. When passing constant gamma is larger than the critical value, the jamming transitions occur from the uniform traffic flow, through the chaotic density wave flow, to the kink density wave flow, with an increasing delay time. The chaotic region increases with passing constant gamma. The neutral stability line is derived from the linear stability analysis. The neutral stability line coincides with the transition line between the uniform traffic and density wave flows. The modified Korteweg-de Vries equation describing the kink jam is derived for small values of gamma by use of a nonlinear analysis.

Journal Article↗