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PubMed2006

Cole-Cole law for critical dynamics in glass-forming liquids.

Within the mode-coupling theory (MCT) for glassy dynamics, the asymptotic low-frequency expansions for the dynamical susceptibilities at critical points are compared to the expansions for the dynamic moduli; this shows that the convergence properties of the two expansions can be quite different. In some parameter regions, the leading-order expansion formula for the modulus describes the solutions of the MCT equations of motion outside the transient regime successfully; at the same time, the leading- and next-to-leading-order expansion formulas for the susceptibility fail. In these cases, one can derive a Cole-Cole law for the susceptibilities; and this law accounts for the dynamics for frequencies below the band of microscopic excitations and above the high-frequency part of the alpha peak. It is shown that this scenario explains the optical-Kerr-effect data measured for salol and benzophenone (BZP). For BZP it is inferred that the depolarized light-scattering spectra exhibit a wing for the alpha peak within the Gigahertz band. This wing results from the crossover of the von Schweidler law part of the alpha peak to the high-frequency part of the Cole-Cole peak; and this crossover can be described quantitatively by the leading-order formulas of MCT for the modulus.

Journal Article↗
PubMed1991

[Unequal crossing-over in conjugated crossings in Escherichia coli K-12].

A genetic model has been developed allowing to study non-equal crossingover in conjugative crossings of Escherichia coli. The model is based on obtaining tandem duplications in the region of the deo operon of E. coli in conjugative crosses Hfr x Hfr. It was shown that when using transposon (Tn5, Tn10) genetic markers the majority of recombinant progeny phenotypically corresponding to rare 2-crossover and 4-crossover recombinants for the deo operon constitute direct tandem duplications resulting from non-equal interchromosomal exchange. Apart from the deo operon, the duplications obtained cover, in some cases, linked thr and leu loci. In the crosses, where point mutations for genes of the deo operon served as genetic markers, the frequency of duplications' formation was lower than that of rare 2-crossover and 4-crossover recombinants' formation. Evolutionary role of the non-equal crossingover phenomenon in E. coli is discussed.

Crossing Over, Genetic↗
PubMed2004

Rapidly rotating Bose-Einstein condensates in and near the lowest Landau level.

We create rapidly rotating Bose-Einstein condensates in the lowest Landau level by spinning up the condensates to rotation rates Omega > 99% of the centrifugal limit for a harmonically trapped gas, while reducing the number of atoms. As a consequence, the chemical potential drops below the cyclotron energy 2 variant Planck's over 2pi Omega. While in this mean-field quantum-Hall regime we still observe an ordered vortex lattice, its elastic shear strength is strongly reduced, as evidenced by the observed very low frequency of Tkachenko modes. Furthermore, the gas approaches the quasi-two-dimensional limit. The associated crossover from interacting- to ideal-gas behavior along the rotation axis results in a shift of the axial breathing mode frequency.

Journal Article↗
PubMed2006

DNA in nanopores: negative capacitance and delta-relaxation at high frequency.

We measured the high frequency dielectric relaxation behavior of DNA molecules confined in nanopores of polycarbonate membrane. The data revealed the existence of a critical frequency omega(c) approximately GHz at which the ac conductivity showed delta-relaxation. Interestingly, the DNA molecules also exhibited a crossover from positive to negative capacitance corresponding to omega(c). The negative capacitance at the critical frequency suggested a strong inductive behavior of DNA molecules in the high frequency regime. The results are interpreted in terms of the confined geometry of the DNA molecules in the nanopores. The interfacial water H-bonded to DNA played a crucial role in determining the high frequency relaxation of DNA molecules. The results indicated that the DNA in nanopores could be designed for application in high frequency bandpass/notch filters.

Computer Simulation↗
PubMed1980

Clonidine (Dixarit) for menopausal flushing.

Clonidine, 0.05 mg twice daily, was evaluated in a multicentre, randomized, placebo-controlled, double-blind crossover study in 66 patients who had had menopausal flushing for less than 1 year. Although the placebo effect was substantial, clonidine reduced the frequency of attacks significantly more than did placebo. In three of the four trials the patients' comparisons of symptoms before and after crossover indicated significantly greater improvement when the crossover was from placebo to clonidine rather than the reverse. The frequency, severity and duration of attacks were reduced by clonidine in 78%, 89% and 88% of the patients respectively, and by placebo in 50%, 53% and 50%. Side effects were minimal and their pattern was the same for clonidine as for placebo. Clonidine's action as a peripheral vascular stabilizer makes it potentially useful for the treatment of menopausal flushing. It would be prudent to include clonidine at the beginning of treatment so that its efficacy could be assessed in each individual. Its use would enhance the effects of the usual management of the menopausal syndrome, which consists of explanation, reassurance and, sometimes, the use of tranquillizers. Clonidine is a symptomatic medication that makes flushing more tolerable and should reduce the number of patients who would otherwise be exposed to the risks of estrogens.

Adult↗
PubMed1991

[The corpus luteum and progesterone secretion].

The pulsatility of LH secretion has been known only since 1970. The pulsatility of progesterone secretion has now also been shown. The frequency and amplitude of these pulses vary during the three phases of the luteal period. The first or early luteal (EL) phase lasts four days starting from the peak of LH. There is no pulsatility of progesterone during EL. The frequency of LH pulsatility is 103 +/- 8 minutes. The second or mid luteal (ML) phases, from +6 to +9 days after the peak of LH, is characterised by pulses of LH and of progesterone, most often in positive crossover correlation and with 7 to 14 pulses per 24 hours. The frequency of LH pulsatility is 166 +/- 33 minutes according to Filicori. The amplitude of LH secretion is 4 to 40 ng/ml. The third or late luteal (LL) phase, occurring at +11 days before the menstrual period, has the same characteristics in terms of quality but shows variations in frequency and amplitude towards a decrease. Thus the amplitude of progesterone secretion is 2.8 to 9 ng/ml (Veldhuis). In the opinion of clinicians, the corpus luteum is independent up to LH+ 5 days. The injection of hCG during this time is ineffective. A single progesterone level is sufficient if the result is 10 ng/ml or more. The problem remains complex concerning results below 10 ng/ml. The solution suggested for the present is that described by Olive: during ML and/or LL, three samples in the morning at hourly intervals and two endometrial biopsies during two consecutive cycles.

Biopsy↗
PubMed1985

Frequency and types of deletional alpha+-thalassemia in northern Sardinia.

We determined by restriction mapping the frequency of the -alpha 3.7 determinant in a random sample of 48 adults in Northern Sardinia. We found a frequency of 0.18 +/- 0.04 and demonstrated that only type I crossover as determined by Apa I digestion (Higgs et al. 1984) is present. Moreover, we showed that this haplotype is not associated with an Rsa I polymorphism 5' to the alpha 2-globin gene. These data support the hypothesis of a unique origin of this deletion in Sardinia.

Adult↗
PubMed1996

[Variation in the frequency of chronic diseases and risk factors in primary care: 1985-1995].

OBJECTIVE: To study the variation in the frequencies of chronic illnesses in Primary Care between 1985 and 1995. DESIGN: A repeated crossover study, carried out with the same information-gathering procedures in two periods 10 years apart. SETTING: A Family Medicine clinic at a Health Centre. PATIENTS: Frequencies of chronic illnesses, obesity and tobacco addiction in 1,677 patients who attended a Family Medicine clinic between September 1994 and August 1995, were collected. In order to examine the variations, these were compared to the findings of a similar 1985 study of 1,356 patients by the same main researcher and in the same clinic, in which the same diagnostic criteria were used. MAIN RESULTS: Frequencies of almost all chronic illnesses had clearly increased from 1985 (average of 0.88 chronic illnesses per patient) to 1995 (average of 1.99 chronic illnesses per patient), especially in the cancer, Endocrinology, mental disorders, circulatory, respiratory, genito-urinary, skin and muscle-skeleton groups. Variation was not very important in coronary Cardiopathy, Cerebrovascular Accident, chronic Obstructive Pulmonary Disease, peptic ulcer/gastritis/dyspepsia, gall bladder illnesses, Hepatopathies and Renal Lithiasis. CONCLUSIONS: The rising tendency in the frequency of chronic illnesses between 1985 and 1995, with a comparison of comparable and stable series, supposes the need for a significant increase in community social-health resources at the Primary Care level.

Adolescent↗
PubMed1984

Frequent occurrence of a zeta-globin-region deletion in American blacks accounts for a previously-described restriction site polymorphism.

We describe an 11.3 kb deletion within the zeta-globin gene region which was found in 2 of 16 American Black neonates. The deletion is consistent with an unequal crossover between the homologous zeta and psi zeta gene regions, resulting in a shortened Eco RI fragment (17.2 kb) containing a single zeta and the psi alpha, alpha 2, and alpha 1 genes. An earlier report of zeta-region crossovers (1) may have overestimated the size of this fragment by 2 kb. This finding led us to re-evaluate another report which concluded that a 17 kb Eco RI fragment found in 10% of the Black population was the result of a restriction site polymorphism (2). Our data do not substantiate this conclusion and we propose that the high frequency of this shortened fragment is due instead to an unequal crossover. Possible clinical consequences of this deletional event are also discussed.

Black People↗
PubMed2006

Ion relaxation dynamics and nearly constant loss behavior in polymer electrolyte.

The broadband conductive spectroscopy covering the range 10(-2) to 10(6) Hz has been employed to examine both the ionic and the segmental motions in polymer salt complexes (PSCs), consisting of polyethylene oxide (PEO), LiClO4, or LiCF3SO3. The temperature dependence of dc conductivity has been analyzed using Vogel-Tamman-Fulcher (VTF) equation and the results suggest that the temperature dependence of the dc conductivity can be well described in terms of the free volume changes with temperature. The ac conductivity at low temperatures (below 223 K) remains unchanged with the temperature, exhibiting nearly linear frequency dependence. This observation, not previously reported in polymers, indicates clearly that nearly constant loss (NCL) phenomenon, usually observed in glassy and ceramic ion conductors, is also operative in polymer electrolytes. Furthermore, a crossover from a NCL to cooperative ion hopping at higher temperatures in the frequency dependence of the conductivity has been observed. The analysis of the temperature dependence of both dc and ac conductivities demonstrates that there exists a direct correlation between the ionic conductivity and the segmental relaxation processes.

Journal Article↗
PubMed1994

A new pacing algorithm for overdrive suppression of atrial fibrillation. Chorus Multicentre Study Group.

Constant rapid pacing may suppress arrhythmias, but it is usually poorly tolerated in the long term. We report a pilot study of a new pacing algorithm for overdrive suppression of atrial premature complexes (APCs) and atrial fibrillation (AF), which prevents postextrasystolic pauses and varies the pacing rate in response to the frequency of APCs. The algorithm was tested in a multiple crossover study for 24 hours in dual chamber pacemakers implanted in 70 patients. Comparison was made on ambulatory recordings between the number of atrial arrhythmias commencing with the algorithm active and inactive. In all cases, the algorithm functioned as designed. No patient was aware of its operation, and no malignant arrhythmias were induced. The 36 recordings that showed atrial arrhythmia were included for analysis. The effects of the algorithm were: APCs (estimated from pacemaker statistics) reduced in 18 patients, increased in 8 (P = 0.02); atrial salvos reduced in 12, increased in 4 (P = 0.041); and AF reduced in 11, increased in 8 (P = NS). In all patients with frequent AF (> 5 episodes in total), fewer episodes occurred when the algorithm was active. We conclude that the algorithm is safe and well tolerated, reduces atrial ectopic activity, and may reduce the frequency of sustained atrial fibrillation.

Adult↗
PubMed1983

Hydralazine and prazosin in the treatment of hypertension.

We report the results of an observer blind crossover trial in 31 patients with essential hypertension comparing the hypotensive effect of four doses of prazosin and of hydralazine used as the third step of triple therapy and additional data on the efficacy of low dose combinations of these two drugs. Both drugs had an appreciable antihypertensive effect, 1 mg of prazosin being equivalent to 12.5 mg of hydralazine. Increasing the dose of prazosin from 4 to 8 mg twice daily and hydralazine from 50 to 100 mg twice daily did not consistently reduce blood pressure. The combination of the two drugs at low doses resulted in the blood pressure of more patients being controlled (diastolic blood pressure 90 mm Hg or below) than when either drug was used alone at high dose. The symptoms reported by patients were similar for both drugs. The combination did not lead to an increased reporting frequency. The trial demonstrates one of the problems of a crossover study, namely a treatment/period interaction.

Adult↗
PubMed1989

Organ blood flow and cardiovascular effects of high-frequency oscillation versus conventional ventilation in dogs with right heart failure.

Mongrel dogs underwent a large (apex to pulmonary valve) right ventriculotomy to produce right ventricular dysfunction. Right ventriculotomy decreased cardiac output from 2.47 +/- 0.43 to 1.34 +/- 0.16 L/min (p less than .01), increased CVP from 3.7 +/- 1.5 to 8.3 +/- 2.4 mm Hg (p less than .01), and decreased mean systemic arterial pressure (MAP) from 143 +/- 16 to 121 +/- 21 mm Hg (p less than .01). There was no effect on mean pulmonary artery pressure (MPAP) or pulmonary artery occlusion pressure. After stabilization a randomized crossover controlled comparison of conventional mechanical ventilation (CMV) and high-frequency oscillation (HFO) was performed. FIO2, pH, PCO2, core temperature, and preload were held constant. Mean airway pressure (Paw) was 4.8 +/- 0.7 cm H2O on CMV vs. 3.5 +/- 1.0 cm H2O on HFO (p less than .05). There was no difference in PaO2. We found no statistically significant differences between the two modes of ventilation with respect to cardiac output, MAP, MPAP, systemic vascular resistance, and pulmonary vascular resistance. Blood flows to cerebral cortex, renal cortex, adrenal, hepatic artery, left ventricular myocardium, and skeletal muscle were not different when comparing CMV to HFO. Despite the ability to attain equivalent oxygenation and ventilation at lower Paw, HFO offers no hemodynamic advantage over CMV in the presence of right ventricular dysfunction.

Animals↗
PubMed1994

Double-blind crossover trial of metronidazole versus placebo in chronic unremitting pouchitis.

Metronidazole has been used to treat pouchitis, but there are no controlled data that show it is effective. Chronic unremitting pouchitis is a form of the disorder particularly difficult to manage. Diarrhea is the main symptom of pouchitis, which results from acute inflammation of the mucosa of an ileal reservoir. To test the hypothesis that metronidazole (400 mg thrice daily for seven days) is no better than placebo at reducing stool frequency in chronic unremitting pouchitis, a double-blind placebo-controlled crossover study has been performed. Thirteen patients who had undergone restorative proctocolectomy for ulcerative colitis were studied. The diagnosis of pouchitis was based on clinical, endoscopic, and histological criteria. At entry all patients had symptomatic pouchitis and were passing more than six stools/24 hr or had consistently bloody stools with at least four of six endoscopic criteria of mucosal inflammation. The median frequency of defecation decreased by 3 bowel actions/24 hr (conservative 95% confidence intervals 0-4/24 hr) on metronidazole but increased by a median of 1/24 hr on placebo. The difference between the median number of bowel motions, when treatment with metronidazole was compared to placebo, was 4 motions/24 hr (P < 0.05) in favor of metronidazole. There was no significant change in the endoscopic or histological grade of inflammation, in the serum C-reactive protein level, or symptomatic scores. In a parallel study, metronidazole did not alter stool frequency in asymptomatic patients without pouchitis who had endoscopically normal reservoirs (six polyposis, six colitis).(ABSTRACT TRUNCATED AT 250 WORDS)

C-Reactive Protein↗
PubMed1992

Using gadolinium-enhanced magnetic resonance imaging lesions to monitor disease activity in multiple sclerosis.

The highly variable clinical course and the lack of a direct measurement of disease activity have made evaluation of experimental therapies in multiple sclerosis (MS) difficult. Recent studies indicate that clinically silent lesions can be demonstrated by magnetic resonance imaging (MRI) in patients with mild relapsing-remitting MS. Thus, MRI may provide a means for monitoring therapeutic trials in the early phase of MS. We studied 12 patients longitudinally for 12 to 21 months with monthly gadolinium (Gd)-enhanced MRIs. The data have been used to identify the most effective design of a clinical trial using Gd-enhanced lesions as the outcome measure. Frequent ( > 1/mo) Gd-enhancing lesions were observed in 9 of the 12 patients, indicating that the disease is active even during the early phase of the illness. The frequency of the lesions was not constant; there was marked fluctuation in lesion number from month to month. However, the magnitude of the peak number of lesions and the frequency of the peaks varied among patients. Because of this variability, the most effective use of Gd-enhancing lesions as an outcome measure in a clinical trial was a crossover design with study arms of sufficient duration to allow accurate estimation of lesion frequency. Monitoring Gd-enhancing lesions may be an effective tool to assist in the assessment of experimental therapies in early MS.

Adult↗
PubMed2005

Offset recombinant PCR: a simple but effective method for shuffling compact heterologous domains.

DNA shuffling and other in vitro recombination strategies have proven highly effective at generating complex libraries for mutagenesis studies. While most recombination techniques employ DNA polymerases in part of a multi-step process, few seek to exploit the natural recombinogenic tendencies and exponential amplification rates of PCR. Here, we characterize a simple but effective method for using standard PCR to promote high recombination frequencies among compact heterologous domains by locating the domains near one end of the template. In a typical amplification reaction, Pfu polymerase generated chimeric crossover events in 13% of the population when markers were separated by only 70 nt. The fraction of recombinant sequences reached 42% after six consecutive rounds of PCR, a value close to the 50% expected from a fully shuffled population. When homology within the recombinant region was reduced to 82%, the recombination frequency dropped by nearly half for a single amplification reaction and crossover events were clustered toward one end of the domain. Surprisingly, recombination frequencies for template populations with high and low sequence homologies converged after just four rounds of PCR, suggesting that the exponential accumulation of chimeric molecules in the PCR mixture serves to promote recombination within heterologous domains.

DNA Shuffling↗
PubMed1996

Inhaled nitric oxide in term infants with hypoxemic respiratory failure.

OBJECTIVE: To determine whether inhaled nitric oxide (NO) administered during conventional mechanical ventilation could produce improvements in oxygenation and reduce the incidence of meeting extracorporeal membrane oxygenation (ECMO) criteria in infants with hypoxemia. DESIGN: Prospective, randomized, controlled trial. Enrolled infants were assigned to conventional treatment with or without adjunctive inhaled NO. Control infants meeting failure criteria (partial pressure of arterial oxygen (PaO2)<80 mm Hg (10.7 kPa)) were allowed to cross over. Caregivers were not masked to group assignment. SETTING: Neonatal intensive care units at the University of Alabama Hospital and the Children's Hospital of Alabama, October 1993 to May 1994. PATIENTS: Newborn infants, both term and near-term, with PaO2 less than 100 mm Hg (13.3 kPa) who were receiving mechanical ventilation with 100% oxygen. Exclusion criteria included major congenital anomalies, diaphragmatic hernia, profound asphyxia, and significant bleeding. INTERVENTIONS: Inhaled NO was initiated in the NO group at a dose of 20 to 40 ppm and advanced stepwise to 80 ppm if PaO2 remained less than 100 mm Hg (13.3 kPa). OUTCOME MEASURES: Primary outcome variables were treatment failure and meeting of ECMO criteria before crossover. Improvement in oxygenation and ultimate use of ECMO or high-frequency oscillatory ventilation were secondary outcome variables. RESULTS: Seventeen neonates with hypoxemia were enrolled; 16 had echocardiographic evidence of pulmonary hypertension, and eight had extrapulmonary shunting. At 1 hour of treatment, two infants in the NO group responded with increases in PaO2 of more than 100 mm Hg (13.3 kPa); after crossover, two had increases in PaO2 of more than 10 mm Hg (1.3 kPa) and one control infant had an increase in PaO2 of more than 10 mm Hg (1.3 kPa). All control infants met failure criteria and crossed over to receive NO; two had increases in PaO2 of more than 10 mm Hg (1.3 kPa) with NO treatment. Despite initial responses, all subjects in both groups eventually met failure criteria. There were no differences between groups in primary outcome variables. CONCLUSIONS: Although inhaled NO produced a transient improvement in oxygenation in some infants, it did not reduce the incidence of meeting ECMO criteria in this population.

Administration, Inhalation↗
PubMed2003

Bonding of multiple noble-gas atoms to CUO in solid neon: CUO(Ng)n (Ng=Ar, Kr, Xe; n=1, 2, 3, 4) complexes and the singlet-triplet crossover point.

Laser-ablated U atoms co-deposited with CO in excess neon produce the novel CUO molecule, which forms distinct Ng complexes (Ng=Ar, Kr, Xe) with the heavier noble gases. The CUO(Ng) complexes are identified through CO isotopic and Ng reagent substitution and comparison to results of DFT frequency calculations. The U[bond]C and U[bond]O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from neon matrix (1)Sigma(+) CUO values, which indicates a (1)A' ground state for the CUO(Ng) complexes. The CUO(Ng)(2) complexes in excess neon are likewise singlet molecules. However, the CUO(Ng)(3) and CUO(Ng)(4) complexes exhibit very different stretching frequencies and isotopic behaviors that are similar to those of CUO(Ar)(n) in a pure argon matrix, which has a (3)A" ground state based on DFT vibrational frequency calculations. This work suggests a coordination sphere model in which CUO in solid neon is initially solvated by four or more Ne atoms. Up to four heavier Ng atoms successively displace the Ne atoms leading ultimately to CUO(Ng)(4) complexes. The major changes in the CUO stretching frequencies from CUO(Ng)(2) to CUO(Ng)(3) provides evidence for the crossover from a singlet ground state to a triplet ground state.

Journal Article↗