Deuterium NMR spectroscopy has been used to investigate the director dynamics in the nematic liquid crystal, 4-pentyl-4′-cyanobiphenyl, confined between two glass plates and subject to orthogonal ...magnetic and pulsed electric fields. When the pulsed electric field, whose intensity is strong enough to make the director align normal to the magnetic field, is applied to the nematic film, the director moves from being parallel to the magnetic field to being parallel to the electric field. After the pulsed electric field is switched off, the director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the turn-off realignment process as a function of time. With this experimental geometry the director alignment is not unique as it can rotate equally probably clockwise or counterclockwise in this realignment process. That is, the realignment pathway for the director is degenerate, which establishes a director flow pattern. We have studied the time dependence of the director orientation and distribution for the turn-off process. The deuterium NMR spectra corresponding to the director dynamics in the realignment pathways were predicted by a continuum theory analysis including a time dependent viscous torque with an effective rotational viscosity.
With more than 300 million monthly active users, Twitter is a powerful social media tool in healthcare, yet the characterization of an academic healthcare Twitter account remains poor to date. We ...assessed basic gender and geographic data on the account's "followers," as well as categorization of each tweet based on content type. We analyzed the impressions, engagements, retweets, favorites, replies, hashtag clicks, and detail expansions using both Sprinklr and Twitter Analytics. Over a period of 12 months, the account amassed 1,235 followers, with 54 percent being male and 68 percent residing in the United States. Of the 1,635 tweets sent out over the life of the account, we report more than 382,464 impressions, 6,023 engagements, 1,255 retweets, 776 favorites, and 1,654 embedded media clicks in this period. When broken down by tweet category, publication tweets garnered the highest engagement with an estimated mean number of clicks per tweet of 8.2 ± 81.9. Original content had higher total engagement per tweet than retweeted material (2.8 ± 9.2 vs. 0.2 ± 0.9 engagements per tweet; p < 0.0001). Tweets regarding internal, national, and continuing medical education events had similar engagement. Herein is the first publication within the medical literature describing a "case series" of cardiovascular tweets over 12 months. We highlight a rapidly emerging group of interactive followers, a successful means by which to disseminate and engage in breaking topics throughout the cardiovascular field, and the importance of combining physician-led knowledge with intermittent marketing messages.
The static director distribution in thin nematic liquid crystal cells, subject to both electric and magnetic fields, has been investigated using a combination of deuterium nuclear magnetic resonance ...(NMR) spectroscopy and continuum theory in terms of the director distribution function, which gives the probability density for finding the director at a given orientation. A series of deuterium NMR spectra for the nematic liquid crystal, 4-pentyl-d(2)-4'-cyanobiphenyl deuteriated in the α position of the pentyl chain were acquired as a function of the applied electric field. This powerful experimental technique allowed us to observe uniform and nonuniform director alignment depending on the angle between the two fields and their relative strength. On the basis of the detailed experimental results, we have explored the factors that influence the nature of both the uniform and the nonuniform director distributions. We have discussed the questions that are raised by our attempt to understand the static director distribution as a function of the angle between the two fields. We have discovered that the alignment of the director at the surface of the Teflon spacers is essential in addition to the random variation in the cell thickness in order to account for the static director distribution determined from the NMR spectra.
Deuterium NMR spectroscopy has been used to investigate the director dynamics of deuteriated 4-α,α-d
2
-nonyl-4′-cyanobiphenyl, where the director was aligned by an electric field. The electric field ...direction made an angle of 47° with the magnetic field in order to provide a unique alignment pathway; accordingly the director is expected to rotate as a monodomain. The time dependence of the director orientation was investigated at different temperatures. At each temperature in the nematic phase, all of the deuterium NMR spectra indicate that the director was uniformly oriented as a monodomain. It was found that the relaxation time in the smectic A phase is about 1,000,000 times as large as that in the nematic phase. This also results in a strong pretransitional growth of the relaxation time as the transition to the smectic A phase is approached.
We have used deuterium NMR spectroscopy to investigate the director dynamics and equilibrium behaviour in nematic liquid crystals (4-pentyl- and 4-octyl-4′-cyanobiphenyl, (5CB and 8CB), both ...specifically deuteriated) when subject to magnetic and a.c. electric fields. The angle between the magnetic and electric fields can be varied between 0 and 90° and the most common geometry we have used is for an angle of about 45°. For 5CB and 8CB (with positive
and
) the director orientation was measured using time-resolved NMR both when the electric field is applied and when it is turned off. In all cases it was found that the director alignment was uniform and the director relaxation follows closely the predictions of the torque-balance equation given by the Leslie-Ericksen theory. In all these experiments we have employed a 10 kHz electric field; at such a relatively high frequency the director experiences an effectively constant value of the electric field. We have now investigated the behaviour of the nematic director for the two liquid crystals at much lower frequencies of the electric field: several Hz to about 1000 Hz. As before, the director orientation was measured using time-resolved deuterium NMR spectroscopy. We have employed two geometries. In one, the electric and magnetic fields were inclined at ∼50°. We found that the director oscillates between two extreme orientations (determined by the frequency and the field strength) in a plane formed by the magnetic and electric fields. The oscillations were observed to continue for many cycles, indicating that the coherence in the director orientation was not lost during this motion. The director was found to remain uniformly aligned. The two extreme director orientations can also be determined from the NMR spectrum time-averaged over many thousands of cycles of oscillations. At low frequencies (several Hz) these limiting angles are essentially independent of frequency but as the frequency increases so the two angles approach each other and become equal at high frequencies. More recently, we have used a geometry with the angle between the fields of ∼90°. A threshold behaviour is observed in this geometry for the director orientation as a function of the applied voltage. The time-averaged spectra at low frequencies and at certain voltages showed unusual powder-like features. Time-resolved NMR measurements at 40 Hz and different voltages near the threshold value were carried out to understand the oscillatory behaviour which was also simulated. Turn-on and turn-off dynamics at high frequency were conducted revealing intriguing differences between the two pathways for the field-induced relaxation. These results will be discussed and interpreted in terms of the torque-balance equation with a time dependent electric field.
A clinical trial to evaluate the efficiency of oral zinc sulphate in the treatment of cutaneous leishmaniasis was conducted. One‐hundred and four patients with parasitologically proven cutaneous ...leishmaniasis were included in the trial. Patients were assigned randomly to receive 2.5, 5 or 10 mg/kg of zinc sulphate orally, and a control group of patients did not receive any treatment. All patients were followed up for 45 days. At the end of the follow‐up period, lesions were assessed and parasitological proof of cure or otherwise was sought. Results showed that the cure rate for the 2.5 mg/kg group was 83.9%, for the 5 mg/kg treatment group it was 93.1% and for the 10 mg/kg treatment group it was 96.9%. No lesions in the control group showed any sign of healing during the follow‐up period. Therefore, oral zinc sulphate can be recommended as a very safe therapy for cutaneous leishmaniasis.
The response times of liquid crystal display devices are determined by a range of factors but the most important of these is usually the rotational viscosity coefficient, n 1 . In order to understand ...the relationship between molecular structure and viscosity it is of considerable interest to measure this viscosity coefficient for a variety of nematogens. Here we report the determination of n 1 for 4-octyl-4'-cyanobiphenyl-d 2 at two temperatures using deuterium NMR spectroscopy. In these experiments the time taken for the alignment of the director can be changed by a field, either magnetic or electric. To do this the liquid crystal film was enclosed in a cell which allows the application of an electric field within the NMR spectrometer. The rate of director relaxation was followed by recording the deuterium NMR spectrum as a function of time during the process of turning the electric field on or off. We have carried out the experiments for a geometry in which the director orientation with respect to the magnetic field of the spectrometer does not exceed 45. The alignment of the director throughout the relaxation process was observed to be uniform. The director relaxation was found to follow closely the predictions of the torque-balance equation given by the Leslie-Eriksen theory. The relaxation times for the turn-on and turn-off processes were determined from this equation and found to be of the order of 1-2 ms. A knowledge of the anisotropic electric and magnetic susceptibilities then allows the determination of the rotational viscosity coefficient.
The rotational viscosity coefficient of a nematic liquid crystal with a positive diamagnetic susceptibility anisotropy can be determined by monitoring the time dependence of the director orientation ...as it is rotated by a field from a non-equilibrium to the equilibrium state parallel to the field. A variety of techniques is available using different properties to monitor the director orientation as a function of time. Normally these experiments are designed so that the property used to determine the director orientation does not change during the time taken for its measurement. Here using ESR spectroscopy, we explore the benefits of exploiting exactly the opposite situation. That is during the time taken to record the ESR spectrum the director orientation is allowed to change. We have developed both semi-quantitative and quantitative models to allow us to simulate how the form of the spectrum depends on experimental conditions such as the field scan rate. These models have also proved to be valuable in designing the experiment and in analysing the spectra. It seems that this novel ESR experiment provides a valuable route to the field-induced relaxation time and hence to the rotational viscosity coefficient.
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