Structure and dynamics of tail-free discotic liquid crystals: Simulations of fluorinated triphenylene.

Recently, a large family of at least 14 discotic liquid crystals was discovered that are exceptions to the conventional paradigm that discotic mesogens tend to feature long, flexible tails on their periphery. To understand why these materials are liquid crystals, as well as the structural determinants of discotic phase behavior, we studied a group of closely related small tail-free disk-like molecules, including both mesogenic and non-mesogenic compounds differing only in the position of a single fluorine substituent. The rigidity and structural simplicity of these molecules make them well suited to for study by large, fully all-atom simulations. Using a combination of static and dynamic metrics, we were able to identify several key features of the columnar mesophase and, thereby, conclusively identify a columnar liquid crystalline mesophase present in a subset of our systems. Our simulations feature molecules hopping between columns in the columnar mesophase and distinctive molecular rotations in 60° steps about the columnar axis. The ability to create and characterize columnar mesophases in silico provides a potent tool for untangling the structural determinants of liquid crystalline behavior in these and other tail-free discotic liquid crystals.

Second harmonic light scattering induced by defects in the twist-bend nematic phase of liquid crystal dimers.

The nematic twist-bend (NTB) phase, exhibited by certain thermotropic liquid crystalline (LC) dimers, represents a new orientationally ordered mesophase - the first distinct nematic variant discovered in many years. The NTB phase is distinguished by a heliconical winding of the average molecular long axis (director) with a remarkably short (nanoscale) pitch and, in systems of achiral dimers, with an equal probability to form right- and left-handed domains. The NTB structure thus provides another fascinating example of spontaneous chiral symmetry breaking in nature. The order parameter driving the formation of the heliconical state has been theoretically conjectured to be a polarization field, deriving from the bent conformation of the dimers, that rotates helically with the same nanoscale pitch as the director field. It therefore presents a significant challenge for experimental detection. Here we report a second harmonic light scattering (SHLS) study on two achiral, NTB-forming LCs, which is sensitive to the polarization field due to micron-scale distortion of the helical structure associated with naturally-occurring textural defects. These defects are parabolic focal conics of smectic-like "pseudo-layers", defined by planes of equivalent phase in a coarse-grained description of the NTB state. Our SHLS data are explained by a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a linear coupling between the two.

Polar structure of disclination loops in nematic liquid crystals probed by second-harmonic-light scattering.

Angle-resolved, second-harmonic-light scattering (SHLS) measurements are reported for three different classes of thermotropic nematic liquid crystals (NLCs): polar and nonpolar rodlike compounds and a bent-core compound. Results revealing well-defined scattering peaks are interpreted in terms of the electric polarization induced by distortions of the nematic orientational field ("flexopolarity") associated with inversion wall defects, nonsingular disclinations, analogous to Neel walls in ferromagnets, that often exhibit a closed loop morphology in NLCs. Analysis of the SHLS patterns based on this model provides a "proof-of-concept" for a potentially useful method to probe the flexopolar properties of NLCs.

Renal infarction with absolute ethanol.

Selective renal artery catheterization was undertaken in a series of mongrel dogs. Absolute ethanol was injected on a dose/weight ratio. Venous blood ethanol levels were monitored. Pre- and postprocedure angiography was performed to evaluate the effectiveness of the injection. The dogs were subsequently sacrificed and pathologic examination performed. Renal infarction was produced in all animals. Systemic blood alcohol levels remained consistently below established criteria of toxic levels. No evidence of vascular damage in systemic arteries distal to the renal artery was found. Absolute ethanol is apparently a safe and effective method of producing permanent renal infarction.

Renal ablation with absolute ethanol. Mechanism of action.

The mechanism of renal ablation by intra-arterial ethanol was studied in 16 mongrel dogs. Ethanol injection rates were varied, and light and electron microscopic studies were performed to detect early parenchymal changes in the kidneys. Pure ischemic injury was also studied as a control. Findings showed extensive parenchymal injury plays a significant role in renal ablation with permanent thrombosis as a delayed event. Acute arterial occlusion occurred with slow ethanol injection rates due to embolization by damaged blood components.

Acute and chronic traumatic arteriovenous fistulae in civilians. Epidemiology and treatment.

Traumatic arteriovenous fistula (AVF) is an uncommon form of vascular disruption. We reviewed 70 AVFs in 69 patients. Nearly one in ten acute arterial injuries is an AVF. Only half of these lesions, however, are clinically demonstrable. Iatrogenic lesions were present in 13% of patients. Eighty-one percent of lesions were treated surgically. Extracranial-intracranial (EC-IC) vascular bypass was used in over one third of head and high neck AVFs. Embolization was used as an adjunct to surgery in about one fourth of patients, and fewer than one in ten were treated with embolization alone. Since half of these lesions are not clinically detectable, liberal use of angiography is necessary for all traumatic wounds in proximity to a major vascular structure. Embolization was useful both as a primary treatment of AVF and as an adjunct to surgery; EC-IC bypass facilitates treatment of inaccessible fistulae in the head and neck.

New instrument for rapid hemostasis and division of small vessels.

A new, finely machined surgical instrument is now available for use in placing two hemostatic metal clips at the same time. The instrument eliminates the need for reloading and handling of a second instrument by the surgeon. This instrument, a new version of the classic, clinically proven Weck Hemoclip clips, should revolutionize the technique of ligation and division of small, fragile blood vessels.

Transhepatic embolization in patients with acute variceal hemorrhage.

Control of acute variceal bleeding by transhepatic embolization was investigated in 14 patients with alcoholic liver disease. In these patients hemorrhage was unresponsive to general supportive measures, intravenous vasopressin and balloon tamponade. Embolization was performed using Gelfoam and a synthetic polymer, bucrylate. Acute hemorrhage was arrested in 86 percent of patients. Rebleeding after transhepatic embolization occurred in 35 percent of patients. There were three deaths from intraabdominal hemorrhage related directly to transhepatic embolization (21 percent). Six patients (43 percent) left the hospital alive. In a group of cirrhotic patients in whom transhepatic embolization was employed after traditional modes of therapy had failed to control variceal hemorrhage, mortality and rebleeding rates were high.

Thoracoscopy for spontaneous pneumothorax 2.10 version with bleb stapling and pleurectomy.

A series of 25 Thoracoscopy procedures were performed for spontaneous pneumothorax over the past 2 1/2 years. The indications for the procedure were recurrent pneumothorax or choice of patient for definitive care. The procedure developed over the period of 2 1/2 years, and the procedure included a thoracoscopy, stapling of apical blebs, and apical pleurectomy. The complication rate was 3% and limited to local wound problems. There was one recurrent pneumothorax in a patient who did not have the pleurectomy as a part of the procedure. This was early on in the experience, when it was felt that pleural abrasion would be adequate. Since that time, a formal apical pleurectomy has been done with each of these procedures. No further recurrences have been noted over the 2 1/2 year period of time. The procedure includes one port at the anterior axillary line, fifth intercostal space, one port in the axilla, third intercostal space, and one port in the midclavicular line, fourth intercostal space. A 30 degree and angled scope is sometimes used for better visualization. The Endo GIA (US Surgical or equivalent Ethicon stapler) is used to staple the blebs, and the pleurectomy is done through the two non-video ports.