The liquid-crystal dimer 1'',7''-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB) exhibits two liquid-crystalline mesophases on cooling from the isotropic phase. The high-temperature phase is nematic; the ...identification and characterization of the other liquid-crystal phase is reported in this paper. It is concluded that the low-temperature mesophase of CB7CB is a new type of uniaxial nematic phase having a nonuniform director distribution composed of twist-bend deformations. The techniques of small-angle x-ray scattering, modulated differential scanning calorimetry, and dielectric spectroscopy have been applied to establish the nature of the nematic-nematic phase transition and the structural features of the twist-bend nematic phase. In addition, magnetic resonance studies (electron-spin resonance and (2)H nuclear magnetic resonance) have been used to investigate the orientational order and director distribution in the liquid-crystalline phases of CB7CB. The synthesis of a specifically deuterated sample of CB7CB is reported, and measurements showed a bifurcation of the quadrupolar splitting on entering the low-temperature mesophase from the high-temperature nematic phase. This splitting could be interpreted in terms of the chirality of the twist-bend structure of the director. Calculations using an atomistic model and the surface interaction potential with Monte Carlo sampling have been carried out to determine the conformational distribution and predict dielectric and elastic properties in the nematic phase. The former are in agreement with experimental measurements, while the latter are consistent with the formation of a twist-bend nematic phase.
Endothelial function is impaired in patients with diabetes mellitus. However, the factors contributing to this defect are currently unknown. Hyperglycemia attenuates endothelium-dependent relaxation ...in normal rabbit arteries in vitro and rat arterioles in vivo. Accordingly, this study examined the effect of acute hyperglycemia on endothelium-dependent vasodilation in nondiabetic humans in vivo.
Endothelium-dependent vasodilation was assessed through brachial artery infusion of methacholine chloride both before and during 6 hours of local hyperglycemia (300 mg/dL) achieved by intra-arterial infusion of 50% dextrose. Forearm blood flow was determined by plethysmography. In a group of 10 subjects, there was a trend toward attenuated methacholine-mediated vasodilation during hyperglycemia compared with euglycemia (P=.07 by ANOVA; maximal response, 13.3+/-2.8 versus 14.7+/-1.5 mL x min(-1) x 100 mL(-1), respectively). In these subjects, the systemic serum insulin levels increased significantly during the dextrose infusion (P<.001). To eliminate the confounding vasoactive effects of insulin, the protocol was repeated during systemic infusion of octreotide (30 ng x kg(-1) x min(-1)) to inhibit pancreatic secretion of insulin. In these subjects (n=10), hyperglycemia significantly attenuated the forearm blood flow response to methacholine (P<.01 by ANOVA; maximal response, 16.9+/-2.5 before versus 12.7+/-1.8 mL x min(-1) x 100 mL(-1) during hyperglycemia). Methacholine-mediated vasodilation was not attenuated by an equimolar infusion of mannitol (P>.40), nor did hyperglycemia reduce endothelium-independent vasodilation to verapamil (P>.50).
Acute hyperglycemia impairs endothelium-dependent vasodilation in healthy humans in vivo. This finding suggests that elevated glucose may contribute to the endothelial dysfunction observed in patients with diabetes mellitus.
Here we report the chemical induction of the twist-bend nematic phase in a nematic mixture of ether-linked liquid crystal dimers by the addition of a dimer with methylene links; all dimers have an ...odd number of groups in the spacer connecting the two mesogenic groups. The twist-bend phase has been identified from its optical texture and x-ray scattering pattern as well as NMR spectroscopy, which demonstrates the phase chirality. Theory predicts that the key macroscopic property required for the stability of this chiral phase formed from achiral molecules is for the bend elastic constant to tend to be negative; in addition the twist elastic constant should be smaller than half the splay elastic constant. To test these important aspects of the prediction we have measured the bend and splay elastic constants in the nematic phase preceding the twist-bend nematic using the classic Frederiks methodology and all three elastic constants employing the dynamic light scattering approach. Our results show that, unlike the splay, the bend elastic constant is small and decreases significantly as the transition to the induced twist-bend nematic phase is approached, but then exhibits unexpected behavior prior to the phase transition.
The twist-bend nematic phase Cifelli, M.; Domenici, V.; Dvinskikh, Sergey ...
Liquid crystals,
2017, Volume:
44, Issue:
1
Journal Article
Peer reviewed
Open access
Recently, there has been a surge of interest in mesogens exhibiting the twist-bend nematic (N-TB) phase that is shown to be chiral even though formed by effectively achiral molecules. Although it now ...seems to be clear that the N-TB phase in the bulk is formed by degenerate domains having opposite handedness, the presence of a supramolecular heliconical structure proposed in the Dozov model has been contradicted by the Hoffmann et al. model in which the heliconical arrangement is replaced by a polar nematic phase. The evidence in support of this is that the quadrupolar splitting tensor measured in various experiments is uniaxial and not biaxial as expected for the twist-bend nematic structure. In this debate, among other evidence, the molecular translational diffusion, and its magnitude with respect to that in the nematic phase above the N-TB phase, has also been invoked to eliminate or to confirm one model or the other. We attempt to resolve this issue by reporting the first measurements of the translational self-diffusion coefficients in the nematic and twist-bend nematic phases formed 1 '',7 ''-bis-4-(4'-cyanobiphenyl-4'-yl) heptane (CB7CB). Such measurements certainly appear to resolve the differences between the two models in favour of that for the classic twist-bend nematic phase. GRAPHICS .
Recently, there has been a surge of interest in mesogens exhibiting the twist-bend nematic (N sub(TB)) phase that is shown to be chiral even though formed by effectively achiral molecules. Although ...it now seems to be clear that the N sub(TB) phase in the bulk is formed by degenerate domains having opposite handedness, the presence of a supramolecular heliconical structure proposed in the Dozov model has been contradicted by the Hoffmann et al. model in which the heliconical arrangement is replaced by a polar nematic phase. The evidence in support of this is that the quadrupolar splitting tensor measured in various experiments is uniaxial and not biaxial as expected for the twist-bend nematic structure. In this debate, among other evidence, the molecular translational diffusion, and its magnitude with respect to that in the nematic phase above the N sub(TB) phase, has also been invoked to eliminate or to confirm one model or the other. We attempt to resolve this issue by reporting the first measurements of the translational self-diffusion coefficients in the nematic and twist-bend nematic phases formed 1 double prime ,7 double prime -bis-4-(4'-cyanobiphenyl-4'-yl) heptane (CB7CB). Such measurements certainly appear to resolve the differences between the two models in favour of that for the classic twist-bend nematic phase.
Background:
Hypospadias is a congenital abnormality of anterior urethral and penile development where the urethral meatus is ectopically located on the ventral aspect of the penis. It is a relatively ...common condition affecting ~1 in 250 male birth. Extended-Tubularized Incised Plate (E-TIP) is a modification of Snodgrass repair by extending the midline incision to the apical part of the glans resulting in a more normal appearing location of the meatus and straight urinary stream without increasing the risk of complications.
Aim of study:
To evaluate functional and cosmetic outcomes of E-TIP repair for mid-shaft and distal hypospadias as a modification of Snodgrass repair.
Patient and method:
A prospective cross-sectional study including 53 cases of mid-to-distal hypospadias repaired with the E-TIP technique between November 2019 and February 2022 in Baghdad. The authors start with the standard technique described by Snodgrass, but the midline incision of the urethral plate extended up to the apical part of the glans tip, and tabularization started distally creating a slit-like a neomeatus. Outcome assessment depended on an objective evaluation of the following parameters: maximum flow rate, post-void residual, Hypospadias Objective Score Evaluation (HOSE) score, and direction of the urinary stream.
Results:
The mean age was 3.4±2.1 years, ranging from 0.6 to 9 years. The mean duration of follow-up was 14.4±6.9 months, and the location of the meatus was coronal in 16 patients (30%), subcoronal in 25 (47%), and mid-distal shaft in 12 (23%). The glans width was greater than or equal to 14 mm in 46 patients (87%) and less than 14 mm in 7 (13%). Q.max was above the fifth percentile of age-related uroflowmetry nomograms for healthy children 5–15 years old in 29 boys (93.5%) and below the fifth percentile in 2 (6.5%). Post-void residual urine was less than 10% of voided volume in 28 out of 31 boys (90%) and greater than 10% in 3 (10%). Regarding cosmetic outcomes, 50 boys (94%) had good penile appearance and their HOSE score greater than or equal to 14 with a slit-like meatus located at the tip of the glans, while 3 (6%) of them their score was less than 14. The overall mean HOSE score postoperatively for all patients was 15±0.9. Six patients (11%) had a deviated urinary stream and 47 (89%) had a straight stream.
Conclusion:
E-TIP repair is a good alternative to standard Snodgrass repair for mid-shaft to distal hypospadias with a good functional and cosmetic outcome, particularly the neomeatus position at the tip of the glans, which is similar to the normal one without increasing the risk of meatal stenosis.
Certain physical properties of nematics can be obtained from the field-induced static and dynamic director orientations in thin films. Here we describe how deuterium nuclear magnetic resonance (NMR) ...spectroscopy can be used to investigate the field-induced director orientation in nematic liquid crystals. This powerful approach is illustrated with specifically deuteriated 4-pentyl-4′-cyanobiphenyl (5CB) subject to the magnetic field of the spectrometer and an electric field applied at an angle to it. A series of deuterium NMR spectra was acquired as a function of the applied electric field, which can be used to explore the static director orientation. When the electric field is applied to the nematic, the director moves from being parallel to the magnetic field to being at an angle to it (the turn-on process) because
and
are both positive for 5CB. After the electric field is switched off, the director relaxes back to being parallel to the magnetic field (the turn-off process). Deuterium NMR spectra were recorded during the turn-on and the turn-off alignment processes as a function of time. Analysis of these results for the static and dynamic experiments, based on the predictions of continuum theory, provides the physical properties of the nematic.
Serratospiculum species were diagnosed in 1360 of 7200 falcons examined over a period from September 2003 to September 2008. The incidence of serratospiculosis was higher in saker falcons (Falco ...cherrug) and peregrine falcons (Falco peregrinus). Serratospiculosis was diagnosed singly in 467 falcons, and in combination with other internal parasites in 893 falcons. Of the falcons diagnosed with only serratospiculosis, 286 showed no clinical signs and 181 showed mild to moderate clinical signs, including dyspnoea. In 126 of the symptomatic falcons, other signs were reported that were difficult to detect on clinical examination. These included inappetence, unsatisfactory weight gain and rapid exhaustion. Fenbendazole at 30 mg/kg bodyweight orally for five to eight days was effective in eliminating eggs and larvae in faeces. No side effects were noticed during or after fenbendazole treatment.
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