Director configuration in the twist-bend nematic phase of CB11CB

The director distribution in the nematic phases exhibited by the 100,1100-bis(4-cyanobiphenyl-40-yl)undecane (CB11CB) liquid crystal has been studied in the bulk with the EPR spin probe technique. EPR spectra confirmed the presence of an higher temperature uniaxial nematic phase and of a lower temperature nematic phase in which the director distribution is not uniform. Spectra recorded in the lower temperature nematic phase were not fully compatible with theoretical EPR spectra calculated according to the recently proposed model for the twist-bend phase in which the local domain director twists around an axis with a fixed tilt angle, θ₀, but were well described by a “distributed-tilt” model in which the director has a relatively narrow distribution, centred at θ₀

EPR study of the polydomain structure of the twist-bend nematic phase of CB9CB in the bulk

EPR spin probe spectra of the liquid crystal phases exhibited, in the bulk, by the 1″,9″-bis(4-cyanobiphenyl-4’-yl)nonane (CB9CB) bent-shape dimer showed that, on cooling from the isotropicphase, this material forms a uniaxial nematic phase with a uniform director macroscopicallyaligned along the spectrometer field. Upon further cooling, a transition into the twist-bendnematic phase is observed after a biphasic region of approximately 4 K. In this lower temperaturenematic phase, the director does not appear to be macroscopically aligned. The non-uniformdirector distribution is modelled as a collection of monodomains tilted with respect to themagnetic field and orientationally distributed around the tilt direction

Microcirculatory changes and skeletal muscle oxygenation measured at rest by non-infrared spectroscopy in patients with and without diabetes undergoing haemodialysis

Introduction: Haemodialysis has direct and indirect effects on skin and muscle microcirculatory regulation that are severe enough to worsen tolerance to physical exercise and muscle asthenia in patients undergoing dialysis, thus compromising patients' quality of life and increasing the risk of mortality. In diabetes these circumstances are further complicated, leading to an approximately sixfold increase in the incidence of critical limb ischaemia and amputation. Our aim in this study was to investigate in vivo whether haemodialysis induces major changes in skeletal muscle oxygenation and blood flow, microvascular compliance and tissue metabolic rate in patients with and without diabetes. Methods: The study included 20 consecutive patients with and without diabetes undergoing haemodialysis at Sant Andrea University Hospital, Rome from March to April 2007. Near-infrared spectroscopy (NIRS) quantitative measurements of tissue haemoglobin concentrations in oxygenated [HbO(2)] and deoxygenated forms [HHb] were obtained in the calf once hourly for 4 hours during dialysis. Consecutive venous occlusions allowed one to obtain muscular blood flow (mBF), microvascular compliance and muscle oxygen consumption (mVO(2)). The tissue oxygen saturation (StO(2)) and content (CtO(2)) as well as the microvascular bed volume were derived from the haemoglobin concentration. Nonparametric tests were used to compare data within each group and among the groups and with a group of 22 matched healthy controls. Results: The total haemoglobin concentration and [HHb] increased significantly during dialysis in patients without and with diabetes. Only in patients with diabetes, dialysis involved a [HbO(2)], CtO(2) and mVO(2) increase but left StO(2) unchanged. Multiple regression analysis disclosed a significant direct correlation of StO(2) with HbO(2) and an inverse correlation with mVO(2). Dialysis increased mBF only in diabetic patients. Microvascular compliance decreased rapidly and significantly during the first hour of dialysis in both groups. Conclusions: Our NIRS findings suggest that haemodialysis in subjects at rest brings about major changes in skeletal muscle oxygenation, blood flow, microvascular compliance and tissue metabolic rate. These changes differ in patients with and without diabetes. In all patients haemodialysis induces changes in tissue haemoglobin concentrations and microvascular compliance, whereas in patients with diabetes it alters tissue blood flow, tissue oxygenation (CtO(2), [HbO(2)]) and the metabolic rate (mVO(2)). In these patients the mVO(2) is correlated to the blood supply. The effects of haemodialysis on cell damage remain to be clarified. The absence of StO(2) changes is probably linked to an opposite [HbO(2)] and mVO(2) pattern

Assessing Skeletal Muscle Variations in Microvascular Pressure and Unstressed Blood Volume at the Bedside

Objective: Quantitative NIRS measurements for MBV partitioning inside microvessels are of current physiologic and clinical interest. In this study, in healthy subjects, we sought new bedside NIRS variables for noninvasively measuring Vu and Pi changes. Methods: Fifteen healthy subjects underwent graded venous congestion for MBV measurements with NIRS and the reference technique strain-gauge plethysmography. From DMBV we calcu- lated vascular compliance, blood flow, and new NIRS variables including Vu and Pit and Pcrit. Results: Extrapolating MBV changes to 0 yielded Pit 4.19 ` 0.5 mmHg corresponding to a Vu of 2.53 ` 0.43 mL/ 100 mL T. The slope for MBV began steeper at values below 18 mmHg (Pcrit). Microvascular compliance measured with NIRS or with strain gauge gave matching results. The change in MBV depended on the oxyhemoglobin increase. No correlation was found between Vu and microvascular compliance or the overall DMBV. Cumulative pressure steps showed higher linearity in DMBV than that induced by discontinuous steps. Conclusions: The new NIRS variables we report could be a practical bench-to-bedside tool to assess venous driving pressure for systemic perfusion and measure changes in Vu within the microvascular bed

Order and Mobility of the Fluorescent Probe 1,6-Diphenylhexatriene in a Polyester Liquid Crystal Polymer

We have employed time dependent fluorescence polarization to investigate a main chain semiflexible polyester type liquid crystal polymer using the fluorescent probe 1,6-diphenylhexatriene. We have obtained the second rank order parameter and the tumbling reorientationaltime of the probeas a functionof temperature. Wehave found the polymer disordering to occur in a temperature range very close to the nematic-isotropic transition