Search

Presents a study that investigated the frequency selection and transient dynamics in single-mode semiconductor lasers with optical feedback. Analysis of the individual switch-on events in the laser; Calculation of the steady-state spectra; Examination of the transient intensity and frequency statistics.

Three microbial enzymatic activities involved in organic matter transformation (Leucine AminoPeptidase, LAP, β-glucosidase, β-GLU and Alkaline Phosphatase, AP) and prokaryotic abundance were studied in the Straits of Messina upwelling system. Samplings were performed monthly, between June 2003 and March 2004, at three stations with different hydrodynamic patterns. Potential hydrolysis rates were estimated using specific fluorogenic substrates. Unlike total prokaryotic abundances, quite spatially homogeneous, enzymatic values described different scenarios for each examined station. At the southern Sicilian side (Scaletta) the highest average activity rates were recorded (LAP: 72.19 ± 19.14 nmol Cleudm−3h−1, β-GLU, 12.53 ± 3.15 nmol Cgludm−3h−1, AP, 113.59 ± 35.47 nmol PO4dm−3h−1), while at the Calabrian side (Pellaro) the minimum values of LAP, β-GLU and AP were measured. Enzymatic activity values showed seasonal patterns everywhere, with summer values which were one order of magnitude higher than those recorded in other seasons and autumn values which sharply decreased. During winter, the enhanced rates of β-GLU and AP suggested the occurrence of active polysaccharide decomposition and phosphorus regeneration. The variability in the enzymatic activity patterns recorded in the Straits area was indicative of biogeochemical features differing among the examined stations; this resulted in changes in the balance between production and decomposition processes. [ABSTRACT FROM AUTHOR]

In Fricke-agarose gels, an accurate determination of the spatial dose distribution is hindered by the diffusion of ferric ions. In this work, a model was developed to describe the diffusion process within gel samples of finite length and, thus, permit the reconstruction of the initial spatial distribution of the ferric ions. The temporal evolution of the ion concentration as a function of the initial concentration is derived by solving Fick's second law of diffusion in two dimensions with boundary reflections. The model was applied to magnetic resonance imaging data acquired at high spatial resolution (0.3 mm) and was found to describe accurately the observed diffusion effects. [ABSTRACT FROM AUTHOR]

A faecal pollution monitoring of coastal Messina waters was performed by comparing three (microscopic, enzyme, and culture) methods. Evidence of Escherichia coli cells (29.99 to 96.79% of the total enteropathogenic serotypes) retaining their viability into the marine environment was shown. β‐Glucuronidase activity rates suggested that living cells were also metabolically active. Heavily polluted sites were detected, where improperly treated urban wastes were discharged. Significant relationships between microscopic and enzymatic data proved both methods to be suitable alternatives to the culture method for E. coli detection, improving environmental quality assessment. [ABSTRACT FROM AUTHOR]

Studies the elimination of Citrus psorosis virus (CPV) by somatic embryogenesis from stigma and style cultures. CPV detection; Loss of juvenile characters in the first year of growth; Germination of somatic embryos; Potential of somatic embryogenesis as a technique for the production of health citrus stocks.

We apply the dynamical mean field theory to calculate the low-density limit of the small polaron optical conductivity in the Holstein model. Classical schemes of approximation are recovered in weak coupling and in the adiabatic and antiadiabatic strong coupling limits. Such schemes are not suitable for the intermediate coupling regime, where our theory gives an anomalous behaviour of the spectral weight at low energy as the temperature decreases. [ABSTRACT FROM AUTHOR]

Objective: To investigate the effects of carvedilol therapy on autonomic cardiovascular regulation and baroreflex sensitivity, by short-term spectral analysis of heart rate (R-R) and systolic blood pressure (S-S) variability. Patients and Methods: The trial was conducted in 12 adults (seven men and five women, mean age 37 ± 7 years) with newly diagnosed hypertension. Patients were classified as having mild or moderate hypertension (stages I to II). R-R, S-S and respiratory signals were recorded during rest and after sympathetic activation by head-up tilt, before and after receiving a 15-day course of carvedilol (25mg once daily). Cross-spectral analysis of R-R and S-S signals was used to determine the baroreflex sensitivity index (α index). Results: At rest after carvedilol therapy, the R-R and S-S LF (low frequency) normalised units (nu) significantly decreased (p = 0.0002 and p = 0.003, respectively), while the HF (high frequency) component reciprocally increased. The R-R LF/HF ratio decreased significantly (1.28 ± 1.58 vs 0.41 ± 0.29, p = 0.008). The α index also increased significantly (12.04 ± 6.25 vs 16.05 ± 7.45, p = 0.002). During tilt, carvedilol therapy reduced the R-R and S-S LF (p = 0.0003 and 0.002, respectively), but preserved the LF increase normally induced by passive orthostatism, and significantly increased the α index (6.18 ± 1.97 vs 8.89 ± 3.29, p = 0.014). Conclusion: Our findings suggested that carvedilol attenuates cardiovascular sympathetic responsiveness and improves baroreflex sensitivity. [ABSTRACT FROM AUTHOR]

Embryo development in vivo has been studied in four Citrus aurantium L. polyembryonic genotypes. Seeds were collected 65, 85, 105, 125 and 220 days after pollination (DAP). None of the immature seeds harvested 65 and 85 DAP contained visible embryos. A single embryo at a more advanced developmental stage was observed in the central position at the micropylar apex of the embryo sac in about 74% of seeds harvested at 105 DAP, while at 125 and 220 DAP the majority of seeds had two or more embryos at the same developmental stage crowded together. Restriction fragment length polymorphism (RFLP) analysis of low- and high-copy-number nuclear DNA was used to distinguish zygotic from nucellar seedlings, Analysis of plantlets derived from in vitro culture of the bigger embryos, located in the central position at the micropylar apex of the embryo sac of seeds harvested at 105 DAP, established that the frequencies of zygotic embryos ranged from 82 to 88%. Media for immature embryo germination in vitro were based on the nutrients and vitamins of Murashige and Skoog (MS) and Murashige and Tucker (MT) media supplemented with various concentrations of sucrose and growth regulators. A total of 76% of globular stage embryos (<0.3 mm) germinated on MT medium containing 150mM sucrose and 14.4 μM gibberellic acid. Heart stage embryos (0.3 - 0.8 mm) germinated at 95% on MT medium supplemented with 150mM sucrose and 2.9 μM gibberellic acid. The addition of 500 mg/I malt extract to MS medium increased the germination of early cotyledon stage (0.8-2.0 mm) embryos to 98%. The optimum sucrose concentration for embryo rescue was 150 mM for the three embryo developmental stages. The ability to form plants in vitro strongly increased with increasing embryo developmental stage. [ABSTRACT FROM AUTHOR]

Ferrous-sulphate infused gels, or 'Fricke gels', encounter great interest in the field of radiation dosimetry, due to their potential for 3D radiation dose mapping. Typically, magnetic resonance (MR) relaxation rates are determined in these systems in order to derive the absorbed dose. However, when large concentration gradients are present, diffusion effects before and during the MR imaging may not be negligible. In these cases, optical techniques may represent a viable alternative. This paper describes research aimed at measuring 3D dose distributions in a Fricke-xylenol orange gel by measuring optical density with a CCD camera. This method is inexpensive and fast. A series of early experiments is described, in which optical density profiles were measured with a commercial microdensitometer for film dosimetry. The light box of the device was modified to work at 567 nm, close to the maximum absorbance of the ferric ion-xylenol orange complex. Under these conditions, the gel shows linearity with dose and high sensitivity. [ABSTRACT FROM AUTHOR]

Somatic embryos were obtained from stylar tissues of three lemon plants, one of cv Lunario, one of Femminello Zagara Bianca, and one of Femminello Santa Teresa. These plants, as shown by visual observations and indexing on woody indicators, were affected by exocortis and two or more virus-like diseases such as psorosis, concave gum, impietratura and cristacortis. Two of the sources contained also mechanically transmissible viruses. Twelve 18-month-old plantlets originating from style culture-derived somatic embryos, four from each source, consistently gave negative reactions when assayed by grafting, mechanical inoculation, and serologically for the presence of viruses, virus-like agents and viroids. It was concluded that, similar to other woody species (e.g. grapevine), somatic embryogenesis opens new possibilities for the sanitary improvement of Citrus. [ABSTRACT FROM AUTHOR]