Temperature dependence of the Landau-Placzek ratio in liquid water.

Rayleigh-Brillouin light scattering is studied in liquid water over the range from 249 to 365 K. Experiments are carried out with a high spectral resolution (0.1 GHz), eliminating any contribution of the structural relaxation to the elastic line. The Landau-Placzek ratio is found as the ratio of the Rayleigh and Brillouin intensities. In the whole temperature range, the Landau-Placzek ratio is found to be in good agreement with a prediction of the theory with a pair of independent thermodynamic variables, pressure and entropy. This description is usually used for single-component homogeneous liquids. An excess of the Landau-Placzek ratio above the prediction is expected for inhomogeneous liquids and is observed, for example, in glass-forming liquids below a certain temperature. In contrast to glass-forming liquids, no excess of elastically scattered light increasing at low temperatures is observed for the Landau-Placzek ratio of water. This suggests that the Landau-Placzek ratio of liquid water can be described by a homogeneous structure, and the idea of the water structure consisting of two structural motifs may not be necessary to explain the experimental ratio.

[Induced expression of Serratia marcescens ribonuclease III gene in transgenic Nicotiana tabacum L. cv. SR1 tobacco plants].

Transgenic Nicotiana tabacum L. cv. SR1 plants, characterized by an increase in the level of dsRNA-specific hydrolytic activity after induction by wounding, were obtained. The Solanum lycopersicum anionic peroxidase gene promoter (new for plant genetic engineering) was for the first time used for the induced expression of the target Serratia marcescens RNase III gene. Upon infection with the tobacco mosaic virus (TMV), the transgenic plants of the obtained lines did not differ significantly from the control group in the level of TMV capsid protein accumulation. In general, no delay in the development of the infection symptoms was observed in transgenic plants as compared with the control group. The obtained transgenic plants represent a new model for the study of the biological role of endoribonucleases from the RNase III family, including in molecular mechanisms of resistance to pathogens.

[Transgenic Expression of Serratia marcescens Native and Mutant Nucleases Modulates Tobacco Mosaic Virus Resistance in Nicotiana tabacum L].

Extracellular Serratia marcescens nuclease is an extremely active enzyme which non-specifically degrades RNA and DNA. Its antiviral activity was previously shown both in animals and in plants when applied exogenously. Transgenic tobacco plants (Nicotiana tabacum L cv. SR1) expressing S. marcescens chimeric, mutant, and intracellular mutant nuclease gene variants were regenerated and challenged with tobacco mosaic virus. The transgenic plants exhibited a higher level of resistance to the virus infection than the control non-transgenic plants. The resistance was evidenced by the delay of the appearance of mosaic symptoms and the retarded accumulation of viral antigen. Thus, these results reveal that modulations of both extracellular nuclease activity and intracellular RNA/DNA binding can protect plants against viral diseases.

Low-frequency inelastic light scattering in a ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass.

Low-frequency (down to 30 GHz) inelastic light scattering is studied in a multicomponent glass ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) in a wide temperature range. The contributions of the THz vibrational spectrum (boson peak) and of the fast relaxation are extracted and analyzed. It is shown that the fast relaxation spectrum is described by a distribution of relaxation times leading to a power-law ν(α) dependence in the frequency range 30-300 GHz. Temperature dependence of α(T) is well described by the Gilroy-Phillips model, while the integrated intensity of the fast relaxation increases significantly with the temperature. This feature distinguishes the fast relaxation in ZBLAN from the case of most single-component glasses. Thermodynamic and kinetic fragility indexes are significantly different for the ZBLAN glass. The correlations between the boson peak intensity, elastic moduli, and fragility index, found earlier for single-component glasses, are fulfilled for the thermodynamic fragility index of ZBLAN. In contrast, the correlation between the fast relaxation intensity at Tg and the fragility holds better for the kinetic fragility index of ZBLAN. We propose that thermodynamic and kinetic fragilities reflect different aspects of glassy dynamics in the case of glass formers with the complex chemical composition and structure topology: the former correlates with the elastic properties and the boson peak, the latter with the relaxation.

Low-frequency Raman scattering in a Xe hydrate.

The physics of gas hydrates are rich in interesting phenomena such as anomalies for thermal conductivity, self-preservation effects for decomposition, and others. Some of these phenomena are presumably attributed to the resonance interaction of the rattling motions of guest molecules or atoms with the lattice modes. This can be expected to induce some specific features in the low-frequency (THz) vibrational response. Here we present results for low-frequency Raman scattering in a Xe hydrate, supported by numerical calculations of vibrational density of states. A number of narrow lines, located in the range from 18 to 90 cm(-1), were found in the Raman spectrum. Numerical calculations confirm that these lines correspond to resonance modes of the Xe hydrate. Also, low-frequency Raman scattering was studied during gas hydrate decomposition, and two scenarios were observed. The first one is the direct decomposition of the Xe hydrate to water and gas. The second one is the hydrate decomposition to ice and gas with subsequent melting of ice. In the latter case, a transient low-frequency Raman band is observed, which is associated with low-frequency bands (e.g., boson peak) of disordered solids.

Glycine phases formed from frozen aqueous solutions: revisited.

Glycine phases formed when aqueous solutions were frozen and subsequently heated under different conditions were studied by Raman scattering, x-ray diffraction, and differential scanning calorimetry (DSC) techniques. Crystallization of ice I(h) was observed in all the cases. On cooling at the rates of 0.5 K∕min and 5 K∕min, glassy glycine was formed as an intermediate phase which lived about 1 min or less only, and then transformed into ß-polymorph of glycine. Quench cooling of glycine solutions (15% w∕w) in liquid nitrogen resulted in the formation of a mixture of crystalline water ice I(h) and a glassy glycine, which could be preserved at cryogenic temperatures (80 K) for an indefinitely long time. This mixture remained also quite stable for some time after heating above the cryogenic temperature. Subsequent heating under various conditions resulted in the transformation of the glycine glass into an unknown crystalline phase (glycine "X-phase") at 209-216 K, which at 218-226 K transformed into ß-polymorph of glycine. The "X-phase" was characterized by Raman spectroscopy; it could be obtained in noticeable amounts using a special preparation technique and tentatively characterized by x-ray powder diffraction (P2, a = 6.648 Å, b = 25.867 Å, c = 5.610 Å, ß = 113.12[ordinal indicator, masculine]); the formation of "X-phase" from the glycine glassy phase and its transformation into ß-polymorph were followed by DSC. Raman scattering technique with its power for unambiguous identification of the crystalline and glassy polymorphs without limitation on the crystallite size helped us to follow the phase transformations during quenching, heating, and annealing. The experimental findings are considered in relation to the problem of control of glycine polymorphism on crystallization.

Raman study of low-frequency modes in three glycine polymorphs.

The temperature dependence of selected low-wavenumber (< 200 cm(-1)) Raman bands was studied for the different crystalline phases (α-, ß-, γ-) of glycine--the simplest possible "building block" of a biomolecule. The temperature dependence of the frequencies of vibrational modes deviates from the theoretical expectation based on the assumption of cubic anharmonicity. Although relatively small, this deviation was observed above 250 K for all the three polymorphs. This finding was discussed in relation to the "dynamical transition" phenomenon, observed in variety of biomolecules in the range 200-250 K. The similarity of the temperatures suggests, that the origin of the dynamical transition phenomenon can be related to intrinsic conformational states of biomolecules, while water serves rather as a plasticizer or a structure organizer.

Transition from single-molecule to cooperative dynamics in a simple glass former: Raman line-shape analysis.

Parameters for orientational and inhomogeneous broadening are found from the line shape analysis of the Raman spectrum of the glass former alpha-picoline during cooling from low-viscous to glassy state. The orientational phase loss time tau(OPL), extracted from the analysis, coincides with the alpha relaxation time at T > T(A), where T(A) is the temperature of transition from an Arrhenius-like to a non-Arrhenius behavior for the alpha-relaxation time dependence on temperature. At lower temperatures tau(OPL) (T) continues the Arrhenius behavior, in contrast to the alpha-relaxation time. The width of inhomogeneous broadening of the Raman line decreases noticeably as temperature increases in the temperature range T(g) < T < T(A), approaching to zero at T approximately T(A). The findings evidence the transition of molecular dynamics from individual to cooperative at T = T(A).

Regulation of intraocular pressure after water drinking.

PURPOSE: Acute oral water loading transiently elevates intraocular pressure (IOP) via mechanisms that remain unexplained. We tested the possibilities that water drinking might elevate IOP by creating a blood-aqueous osmotic gradient, or that it might instead alter active ion pumping and the formation of aqueous humor. METHODS: In the first series, 16 young, healthy individuals were studied during dehydration and for 1 hour after rehydration (14 mL H2O/kg body weight). Hematocrit, total plasma osmolality, and plasma colloid osmotic pressure were determined simultaneously with measurements of IOP. In a second series (N = 16), rehydration occurred after pretreatment with either placebo or a topical carbonic anhydrase inhibitor (1 drop 2% dorzolamide in each eye, 12 and 2 hours before oral water loading). RESULTS: In both series, mean IOP increased significantly 15 minutes after water ingestion and remained elevated above baseline for 45 minutes. In contrast, colloid osmotic pressure and hematocrit were unaltered by water drinking, and neither these variables nor total plasma osmolality correlated with IOP. In the second series, pretreatment with dorzolamide reduced baseline IOP, but failed to alter the magnitude or time course of IOP elevations induced by water drinking. CONCLUSION: Because water drinking failed to create a blood-ocular osmotic pressure gradient, neither vitreous hydration nor increased aqueous ultrafiltration can explain increases in IOP after acute hydration. Because the increase in ocular tension apparently also is independent of active bicarbonate pumping, factors affecting aqueous drainage must explain the water drinking effect.

Mechanism of exercise-induced ocular hypotension.

PURPOSE: Although acute dynamic exercise reduces intraocular pressure (IOP), the factors that provoke this response remain ill-defined. To determine whether changes in colloid osmotic pressure (COP) cause the IOP changes during exercise, standardized exercise was performed after dehydration and hydration with isosmotic fluid. METHODS: Progressive cycle ergometer exercise to volitional exhaustion was performed after 4 hours' dehydration, and after hydration with 946 ml isosmotic liquid (345 mOsM). In each experiment, venous blood taken before and immediately after exercise was analyzed for hematocrit, plasma protein concentration, total plasma osmolality, and plasma COP. RESULTS: Exercise in both experiments significantly reduced IOP and elevated COP (each P < 0.01). Dehydration, compared with hydration, also significantly reduced IOP and elevated COP, when measured before and after exercise (P < 0.05). The correlation of mean IOP with mean COP, over the entire range created by varying exercise and hydration statuses, was statistically significant (r = -0.99; P < 0.001). In contrast, other indexes of hydration status, including hematocrit, total plasma osmolality, and plasma protein concentration, failed to change as IOP changed and failed to correlate with IOP, on either a group or individual basis, in conditions of varying levels of exercise and hydration. CONCLUSIONS: Acute dynamic exercise and isosmotic fluid ingestion each seem to change IOP through changes in COP.

Hypertension and the eye: applications of the Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure.

BACKGROUND: High blood pressure is a major risk factor for coronary artery disease, kidney disease, and stroke. More people are aware of treating and controlling their blood pressure, but overall control rates are low and the incidence of hypertension-related morbidity and mortality remains high. METHODS: The National Heart, Lung, and Blood Institute released The Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC VI) as the most recent national guideline to hypertension control for primary care clinicians. RESULTS: JNC VI identifies 10 hypertension-related public health challenges: (1) prevent the rise of blood pressure; (2) decrease prevalence of hypertension; (3) increase awareness and detection of hypertension; (4) improve control of hypertension; (5) reduce cardiovascular risks; (6) increase recognition of importance of isolated systolic hypertension; (7) improve recognition of importance of high-normal blood pressure; (8) reduce ethnic, socioeconomic, and regional variations; (9) improve treatment; and (10) enhance community programs. CONCLUSIONS: The eye is a target organ and retinopathy is a frequent complication--as well as a prognostic indicator--of sustained hypertension. As part of a multidisciplinary team approach, the optometrist assumes a significant role in the prevention, detection, evaluation, and treatment of high blood pressure and its associated morbidities.

An overview of the Heidelberg Retina Tomograph.

BACKGROUND: The Heidelberg Retina Tomograph (HRT) is a new ophthalmic diagnostic instrument which uses confocal laser scanning microscopy to quantify precisely, in vivo, the topography of the posterior fundus. HRT technology permits accurate, highly reproducible documentation of the posterior fundus, along with software designed for longitudinal study of the optic nerve in glaucoma. This technology provides the practitioner with a new dimension for examination of the posterior fundus. METHODS & RESULTS: The current literature is reviewed to gather information about the HRT technology and its clinical applications. HRT's technology is highly reproducible and accurate, offering many advantages over other imaging techniques for optic nerve head analysis. The ability of the HRT to provide a precise change analysis over time may allow for early detection of subtle alterations in the topography of the optic nerve head before visual field loss occurs. The HRT may also be applied to the topographical analysis of other posterior fundus conditions, such as papilledema, macular edema, macular holes, and tumors. CONCLUSIONS: As with any new instrument, there are many questions regarding confocal laser scanning technology that remain unanswered. Key questions regarding the specific stereometric parameters that are most important for detecting glaucoma and their progression (before conventional photography or visual field testing) remain to be answered. HRT is still a relatively new area of research, and more studies are required.

Clinical implications of intra- and inter-reader agreement in four different automated visual fields.

BACKGROUND: This study was designed and conducted to examine the degree of inter- and intra-reader agreement when four readers evaluate visual fields in patients known to have glaucoma and patients known to not have glaucoma. METHODS: Fifty-three patients known to have glaucoma and 60 patients known not to have glaucoma were selected randomly from a population at the University of Alabama at Birmingham School of Optometry. Four visual fields were performed on each patient, non-dilated, with the proper correction in place. The fields were performed on three different instruments by technicians who were unaware of the diagnostic status of the patient. Four independent (blinded) clinicians read the visual fields and judged them as: "glaucoma field defect," "no glaucoma field defect," and "poor reliability-cannot judge." RESULTS: Statistical analysis revealed that a single reader's interpretation of four different types of visual fields are very different from, are poorer than, and are more consistent than are the four readers' interpretations of a single type of visual field. The analysis also shows that the readers consistently underestimated the number of glaucoma patients with one instrument and overestimated the number with another. CONCLUSIONS: This results suggest that a single visual field will discriminate patients with glaucoma with an accuracy in the 70 to 75 percent range. For one of the instruments, the shorter protocol was almost as effective in discriminating glaucomatous fields as the longer protocol. This study also suggests that repeating the visual fields or analysis of a single field by two readers improves reliability.

Correlates of acute exercise-induced ocular hypotension.

PURPOSE: To understand those factors that determine the decrease in intraocular pressure (IOP) that occurs during acute dynamic exercise. METHODS: Three aspects of the exercise-IOP relationship were studied. These included graded exercise, with and without CO2 addition for isocapnia; comparison of the IOP response of trained and sedentary subjects to a fixed external work load; and exercise after ocular beta-adrenoceptor blockade. Graded exercise consisted of 7 minutes each at 30 and 90 watts on a cycle ergometer, then progressive work to exhaustion. Trained and sedentary subjects were defined on the basis of the blood lactate response to fixed external work (10 minutes at 90 watts). Selective beta 1-adrenoceptor blockade (betaxolol) and nonselective beta-adrenoceptor blockade (levobunolol) were superimposed on graded exercise. Intraocular pressure was measured using applanation tonometry. RESULTS: Graded exercise: Intraocular pressure decreased in proportion to exercise intensity. Hypocapnia developed in the last minutes of exhausting work, but preventing hypocapnia with CO2 addition failed to lessen the decrease in IOP. Response to fixed external work load: Intraocular pressure decreased significantly more in sedentary than in trained subjects; this decline was correlated with elevations in blood lactate but not with changes in metabolic rate or plasma osmolarity. Selective and nonselective beta-adrenoceptor blockade: Both drugs lowered IOP at baseline and throughout graded exercise; the drugs and exercise had apparently additive ocular hypotensive effects. CONCLUSIONS: Acute dynamic exercise lowers IOP in a graded fashion proportional to relative, not absolute, work load. The IOP decline is correlated with blood lactate but not with PCO2 or plasma osmolarity changes, and exercise potentiates the ocular hypotensive effects of beta-adrenoceptor blockade.

Ocular hypotension during short- and long-term hypocapnia.

Severe, short-term decreases in alveolar Pco2 acutely lower intraocular pressure (IOP). We wondered if less severe, physiologically relevant Pco2 reductions would also lower ocular tension and if this effect would persist in the longer term. To investigate the acute influence of small Pco2 changes on IOP, 11 healthy persons hyperventilated to reduce end-tidal Pco2 by first 10% (5 min) and then 20% (5 min). IOP fell when Pco2 fell 20% (14.5 +/- 2.1 mm Hg vs, 16.8 +/- 1.0 in a matched control series; p < 0.05) and remained depressed 20 min after Pco2 had returned to baseline levels. To investigate the persistence over time of this hypocapnia-associated IOP reduction, nine healthy persons hyperventilated to reduce end-tidal Pco2 by 15% for 1 h. IOP was substantially reduced by 30 min (11.7 +/- 0.5 vs. 14.8 +/- 0.6 mm Hg; p < 0.05) and at 60 min (11.2 +/- 0.7 vs. 14.2 +/- 0.6 mm Hg; p < 0.05) of sustained hypocapnia. In contrast, when the effects of acute hypocapnia were compared with standard nonselective beta-adrenergic blockade (levobunolol HC1, 1 drop 0.5% solution instilled 12 and 2 h before study; N = 7 normals), a 20% Pco2 reduction was less effective in lowering IOP than was drug treatment, and induction of hypocapnia failed to alter IOP after drug treatment [baseline IOP 14.4 +/- 1.3 mm Hg vs. 10.0 +/- 1.6 mm Hg after levobunolol (p < 0.05) and 10.7 +/- 1.9 mm Hg after hypocapnia and levobunolol were combined]. In addition, 3 days' treatment with the ventilatory stimulant drug medroxyprogesterone acetate (150 mg/day in 10 men, initial IOP

Diagnosis and management of temporal arteritis: a review and case report.

Temporal arteritis is an insidious disease which, if not recognized and treated with high-dosage oral prednisone or intravenous prednisolone, can result in unilateral or even total blindness due to anterior ischemic optic neuropathy (AION) or closure of the central artery of the retina. Unfortunately, the symptoms and clinical signs of temporal arteritis mimic those of a number of other conditions including angle-closure glaucoma, hypertension, migraine, trigeminal neuralgia, temporomandibular joint syndrome, carotid artery occlusive disease, Foster-Kennedy syndrome, and nonarteritic AION. When a patient complains of a severe pain in the temporal region, along with scalp tenderness and a feeling of malaise or depression--with or without episodes of transient loss of vision--he or she should be referred for a diagnostic work-up which includes an erythrocyte sedimentation rate and a temporal artery biopsy. We present here a review of the recent literature concerning temporal arteritis, followed by a report of an unusual case in which high-dosage prednisone therapy was effective in relieving the patient's symptoms and lowering the sedimentation rate in spite of a negative temporal artery biopsy.

Isocapnia blocks exercise-induced reductions in ocular tension.

Previous reports suggest that isometric exercise (2-min handgrip at 50% maximal voluntary contraction [MVC]) substantially lowers intraocular pressure (IOP). The authors questioned whether the mechanism for lowered IOP in exercise is secondary to hyperventilation. Accordingly, in this study 11 subjects, with elevated IOP (greater than or equal to 18 mm Hg) and otherwise healthy, did 2 min of handgrip exercise at 50% MVC with and without carbon dioxide supplementation to maintain isocapnic conditions. Compared with a control experiment that involved neither exercise nor CO2 addition, exercise induced a fall in IOP from 18.3 to 15.6 mm Hg (P less than 0.001). This statistically significant decline in IOP persisted for 15 min after the exercise session. At the point of minimum IOP (1 min after the end of exercise), the minute ventilation was elevated from 6.5-8.1 l/min (P less than 0.05), and the end-tidal partial pressure of CO2 (PCO2) was reduced from 37.0 to 33.7 mm Hg (P less than 0.05) with respect to control values. By contrast, adding CO2 sufficient to maintain isocapnic conditions (experimental end-tidal PCO2 = 38.9 versus 38.5 mm Hg in the control study; P = not significant) abolished the exercise-induced ocular hypotension (experimental IOP = 17.8 versus 18.1 mm Hg in the control study; P = not significant). It was concluded that prevention of hypocapnia during isometric handgrip exercise blocks the subsequent fall in IOP, suggesting both that isometric exercise per se has no direct influence on IOP and that therapy for ocular hypertension could involve manipulation of blood gases.

Benign essential blepharospasm.

A 57-year-old female had vague visual complaints of pressure behind her right eye during an ocular examination. One month later the patient was visually impaired due to uncontrollable spasms of both eyelids. A diagnosis of benign essential blepharospasm (BEB) was made, and the patient was eventually treated with botulinum toxin to temporarily relieve her symptoms. I have reviewed and summarized the literature relating to the characteristics and management of this often misdiagnosed and misunderstood ocular muscular condition.