Insights into glass surface dynamics from fast scanning calorimetry studies of softening and vaporization of ultrathin molecular films.

Chemical and physical processes on the surfaces of amorphous solids have been the focus of many studies over the past decades. These studies have established that dynamics in a thin layer near a glass surface are often dramatically faster than those in the glass bulk. Nevertheless, recent advances also emphasize the need for new experimental techniques capable of characterizing the structure and dynamics of the near-surface regions in glassy materials at the molecular length scale. Using a quasi-adiabatic fast scanning calorimetry (FSC) technique, we have investigated softening and vaporization of pure amorphous methylbenzene films of moderately heightened kinetic stability with thicknesses ranging from 1 to 20 nm. The analysis of the FSC thermograms reveals the existence of a high fictive temperature (liquid-like) layer on the surface of the solid glass with a thickness of 3.5 ± 0.5 nm or seven molecular diameters. Furthermore, the width of the boundary between liquid-like and solid layers in the films is less than 1 nm. These preliminary findings compliment and substantiate past determinations of the mobile surface layer thicknesses obtained by introduction of nanoparticles or spectroscopic molecular probes to near-surface regions of amorphous samples. The developed FSC methodology will advance the theoretical and computational research by providing calorimetric data on the enhanced interfacial dynamics phenomenon in a variety of low-molecular-weight amorphous materials.

Left cardiac sympathetic denervation in children with Jervell Lange-Nielsen syndrome and drug refractory torsades - A case series.

INTRODUCTION: Long QT syndrome is an inherited malignant channelopathy which leads to life-threatening arrhythmia, with multiple genotypes. Jervell and Lange-Nielsen syndrome (JLNS) is an autosomal recessive subtype of this disease, characterized by congenital sensorineural deafness and a high incidence of sudden cardiac death (SCD). METHODOLOGY: We prospectively followed up six children who underwent left cardiac sympathetic denervation (LCSD) for JLNS in view of high-risk features despite being on maximally tolerated doses of oral propranolol. RESULTS: Mean age at diagnosis was 2.75 ± 0.39 years, with a significant delay between onset of symptoms and diagnosis (mean 7.2 ± 3.5 months). All had sensorineural hearing loss, conforming to the JLNS phenotype. Mean QTc interval was 603 ± 93 ms, with T wave alternans (TWA) seen in all cases. All were started on propranolol and subsequently subjected to LCSD, and 3 underwent AAI permanent pacemaker implantation. Over a mean follow-up of 20 months, there was a significant reduction in QTc (603 ± 93 ms to 501 ± 33 ms, p = .04), which was persistent on follow-up (525 ± 41 ms) and only two out of six had persistent T wave alternans on ECG (p < .01). None of these children had presyncope, syncope, seizures, torsades de pointes, cardiac arrest or death on follow up following LCSD. CONCLUSION: Jervell Lange-Nielsen syndrome is a subtype of LQTS with high-risk features. LCSD, an effective therapeutic option for those having symptoms despite being on propranolol, results in significant reduction of QTc interval and amelioration of symptoms.

Glass softening in the limit of high heating rates: Heterogeneous devitrification kinetics on nano, meso, and micrometer scale.

When heated rapidly, glasses often devitrify heterogeneously, i.e., by a softening front that originates at the surface of an amorphous film. Yet the fundamentals of this devitrification regime are not completely understood; depending on experimental conditions, the reported front propagation distances differ by an order of magnitude. Using a high-resolution fast scanning calorimetry technique, we have investigated the softening of glassy methylbenzene films with thicknesses between 30 and 1400 nm. We confirm first that, in all films, the devitrification process begins with the formation of a softening front that propagates through the films over distances of ∼50 nm and that the front propagation kinetics at this stage follow an Arrhenius law. However, we also show that, in films with thicknesses above 165 nm, the front propagation does not terminate with the onset of bulk softening. Specifically, increasing the films' thicknesses above 165 nm yields sharp, clearly discernible endotherms that precede the bulk softening endotherms and that are consistent with a two-fold increase in the enthalpic barrier to front propagation at a well-defined critical temperature. We term this phenomenon "Arrhenius discontinuity" and use reaction rate and continuum front dynamics theories to explain its origins and the physical nature of the resulting distinct heterogeneous devitrification processes. Finally, we discuss the findings in the context of recent theoretical, computational, and experimental studies of heterogeneous devitrification by other research groups.

Lipomatosis of spinal epidural space, peritoneum, and renal sinus: a rare complication of long-term steroid therapy in a child with nephrotic syndrome.

Excessive visceral adipose tissue proliferation, resulting in diffuse lipomatosis, is a rare complication of long-term steroid therapy. A 10-year-old boy presented with severe radicular back pain with limitation of lower limb movements. He was diagnosed with steroid-resistant nephrotic syndrome and was on unregulated steroid therapy. Magnetic resonance imaging of the spine showed increased adipose tissue in the epidural space of the lumbo-sacral spine causing clumping of cauda equina nerve roots along with marked proliferation of fat in the renal sinus as well as peritoneum. He was started on pregabalin with tapering of steroids, following which there was a gradual decrease in pain and improvement of activity. Our patient had diffuse lipomatosis involving spinal epidural space, bilateral renal sinus, and peritoneum, secondary to steroid overuse. With the availability of advanced imaging techniques, the condition can be prevented by judicious and proper use of steroids with close follow-up for any untoward complications.

Fundamentals and characterizations of scratch resistance on automotive clearcoats.

As original equipment manufacturers (OEMs) strive to deliver improved coating performance with a sustainable footprint, opportunities for innovation are emerging, particularly on improving mechanical properties, appearance, and solids content. Resistance to scratch and mar damage is one of the key performance attributes that has been emphasized by both OEMs and consumers to maintain a vehicle's appearance and corrosion resistance over its service lifetime. Fundamental methodologies including instrumented scratch measurements at multiple size scales are used in this work as part of a product development strategy to better understand the scratch and mar behavior of automotive topcoats. This study compares physical properties of several melamin-formaldehyde and isocyanate cured clearcoats over the appropriate basecoats. Micro- and nano-scratch techniques were employed in combination with industry standard method, Amtec-Kistler carwash to identify performance differences under different scratch conditions. Mechanical and viscoelastic properties of the coatings were studied using tensile tests and dynamic mechanical thermal analysis (DMTA) to better understand the failure mechanisms associated with plastic deformation and fracture at different scratch scales. The information gathered from the above testing protocols is used to analyze coating performance in terms of the contact strain, transitions between elastic - plastic behavior, coefficient of friction and stress localization.

Communication: Surface-facilitated softening of ordinary and vapor-deposited glasses.

A common distinction between the ordinary glasses formed by melt cooling and the stable amorphous films formed by vapor deposition is the apparent mechanism of their devitrification. Using quasi-adiabatic, fast scanning calorimetry that is capable of heating rates in excess of 105 K s-1, we have investigated the softening kinetics of micrometer-scale, ordinary glass films of methylbenzene and 2-propanol. At the limit of high heating rates, the transformation mechanism of ordinary glasses is identical to that of their stable vapor-deposited counterparts. In both cases, softening is likely to begin at the sample surface and progress into its bulk via a transformation front. Furthermore, such a surface-facilitated mechanism complies with zero-order, Arrhenius rate law. The activation energy barriers for the softening transformation imply that the kinetics must be defined, at least in part, by the initial thermodynamic and structural state of the samples.

Melting of superheated molecular crystals.

Melting dynamics of micrometer scale, polycrystalline samples of isobutane, dimethyl ether, methyl benzene, and 2-propanol were investigated by fast scanning calorimetry. When films are superheated with rates in excess of 105 K s-1, the melting process follows zero-order, Arrhenius-like kinetics until approximately half of the sample has transformed. Such kinetics strongly imply that melting progresses into the bulk via a rapidly moving solid-liquid interface that is likely to originate at the sample's surface. Remarkably, the apparent activation energies for the phase transformation are large; all exceed the enthalpy of vaporization of each compound and some exceed it by an order of magnitude. In fact, we find that the crystalline melting kinetics are comparable to the kinetics of dielectric α-relaxation in deeply supercooled liquids. Based on these observations, we conclude that the rate of non-isothermal melting for superheated, low-molecular-weight crystals is limited by constituent diffusion into an abnormally dense, glass-like, non-crystalline phase.

Vapor-deposited non-crystalline phase vs ordinary glasses and supercooled liquids: Subtle thermodynamic and kinetic differences.

Vapor deposition of molecules on a substrate often results in glassy materials of high kinetic stability and low enthalpy. The extraordinary properties of such glasses are attributed to high rates of surface diffusion during sample deposition, which makes it possible for constituents to find a configuration of much lower energy on a typical laboratory time scale. However, the exact nature of the resulting phase and the mechanism of its formation are not completely understood. Using fast scanning calorimetry technique, we show that out-of-equilibrium relaxation kinetics and possibly the enthalpy of vapor-deposited films of toluene and ethylbenzene, archetypical fragile glass formers, are distinct from those of ordinary supercooled phase even when the deposition takes place at temperatures above the ordinary glass softening transition temperatures. These observations along with the absolute enthalpy dependences on deposition temperatures support the conjecture that the vapor-deposition may result in formation of non-crystalline phase of unique structural, thermodynamic, and kinetic properties.

Enthalpy and high temperature relaxation kinetics of stable vapor-deposited glasses of toluene.

Stable non-crystalline toluene films of micrometer and nanometer thicknesses were grown by vapor deposition at distinct rates and probed by fast scanning calorimetry. Fast scanning calorimetry is shown to be extremely sensitive to the structure of the vapor-deposited phase and was used to characterize simultaneously its kinetic stability and its thermodynamic properties. According to our analysis, transformation of vapor-deposited samples of toluene during heating with rates in excess 10(5) K s(-1) follows the zero-order kinetics. The transformation rate correlates strongly with the initial enthalpy of the sample, which increases with the deposition rate according to sub-linear law. Analysis of the transformation kinetics of vapor-deposited toluene films of various thicknesses reveal a sudden increase in the transformation rate for films thinner than 250 nm. The change in kinetics seems to correlate with the surface roughness scale of the substrate. The implications of these findings for the formation mechanism and structure of vapor-deposited stable glasses are discussed.

A case of large aneurysms of the coronary arteries and abdominal aorta in an infant.

Aneurysms of the coronary arteries and abdominal aorta are extremely rare in infancy. Due to the rarity of the anomaly, there are no existing guidelines on management of these aneurysms. We describe the challenges in diagnosis, evaluation and management of an infantile Marfan with this rare presentation.

Aorto-Left Ventricular Tunnel-An Uncommon Entity.

The aorto-left ventricular tunnel is an extracardiac communication that has a specific morphological feature. It is important to differentiate this entity from other diagnoses because the treatment options differ significantly and better outcomes are obtained with this entity.

Long-term outcome of permanent epicardial pacemaker implantation in neonates: Experience from an Indian center.

Introduction: Permanent pacemaker implantation (PPI) in neonates is challenging with respect to indications, device selection, implantation technique, and long-term outcomes. Complex anatomy, the need for long-term pacing with high rates, and a problematic postoperative period are the major problems. Methods: We prospectively followed up 22 newborns who underwent PPI below 28 days of life at our institute. Results: The median age at implantation was 2 days (interquartile range 1-9 days), and 9% were born preterm. The average heart rate before implantation was 46.4 ± 7.2 bpm. Maternal lupus antibodies were positive in 8 (36.4%) neonates, whereas 11 (50.0%) had associated congenital heart disease. Nineteen neonates underwent single chamber (VVI) and three underwent dual chamber (DDD) pacemaker implantation. Over a median follow-up of 46 months (range 2-123 months), the average ventricular pacing percentage was 87.5 ± 24.9%, with a stable pacing threshold. Seven children underwent pulse generator replacement due to battery depletion at a median age of 47 months. Pacing-induced ventricular dysfunction was seen in five children at a median age of 23.6 months, and two underwent upgradation to cardiac resynchronization therapy. Overall mortality was 13.6%, all due to tissue hypoperfusion and lactic acidosis in the postimplantation period. Conclusions: PPI in neonates has a favorable outcome with excellent lead survival. Overall mortality is 13.6%, which is predominantly in the postimplantation period and related to myocardial dysfunction.

Sudden-Onset Blindness in a Child With Hypertensive Emergency: Unmasking of Chronic Kidney Disease.

A 10-year-old male presented with sudden-onset diminution of vision in both eyes. On systemic examination, he had severe hypertension, no pulse deficit, short stature, and no other focal neurological deficit. Dilated fundoscopy showed bilateral grade 4 hypertensive retinopathy with macular star formation. Detailed laboratory investigations revealed a stage 5 chronic kidney disease (CKD). We present this case to highlight this rare ocular manifestation of CKD in pediatric age group.

Recurrent pericardial effusion in a boy: A clue to underlying pericardial and pulmonary lymphangiectasia.

Pulmonary lymphangiectasia is a rare congenital malformation of lymphatic vessels. We report the case of a 5-year-old boy with recurrent pericardial effusion which was diagnosed to be due to pericardial and pulmonary lymphangiectasia.

Pulmonary artery aneurysm: Harbinger of an ominous disease.

An 11-year-old girl presented with chronic cough and recurrent hemoptysis. On examination, she had features of right heart failure and cyanosis, with severe pulmonary hypertension on echocardiogram. Computed tomography pulmonary angiography showed aneurysmal dilatations of the pulmonary artery with elevated erythrocyte sedimentation rate and C-reactive protein and positive human leukocyte antigen B51. A diagnosis of Hughes-Stovin syndrome (vascular variant of Behcet's syndrome) was confirmed, and she was started on immunosuppression, on which there was improvement.

Thrombosis of aneurysmal pulmonary arteries in patent ductus arteriosus with Eisenmenger syndrome.

A 45-year-old lady with patent ductus arteriosus with Eisenmenger's syndrome had presented with hemoptysis. Computed tomography revealed aneurysmally dilated pulmonary arteries with a large calcified organized thrombus.

Bulk and interfacial glass transitions of water.

Fast scanning calorimetry (FSC) was employed to investigate glass softening dynamics in bulk-like and ultrathin glassy water films. Bulk-like water samples were prepared by vapor-deposition on the surface of a tungsten filament near 140 K where vapor-deposition results in low enthalpy glassy water films. The vapor-deposition approach was also used to grow multiple nanoscale (approximately 50 nm thick) water films alternated with benzene and methanoic films of similar dimensions. When heated from cryogenic temperatures, the ultrathin water films underwent a well manifested glass softening transition at temperatures 20 K below the onset of crystallization. However, no such transition was observed in bulk-like samples prior to their crystallization. These results indicate that thin-film water demonstrates glass softening dynamics that are dramatically distinct from those of the bulk phase. We attribute these differences to water's interfacial glass transition, which occurs at temperatures tens of degrees lower than that in the bulk. Implications of these findings for past studies of glass softening dynamics in various glassy water samples are discussed.

'Misplaced' central venous catheter in a newborn: Reminder of a common congenital anomaly.

Left superior vena cava is the commonest congenital anomaly of systemic venous return. We present the case of a newborn where left jugular venous placement of central venous catheter resulted in cannulation of the left superior vena cava.

Ventricular septal defect with pulmonary arterial hypertension in an infant: Is there something more than what meets the eye?

An 11-month-old girl was detected to have muscular ventricular septal defect with hyperkinetic pulmonary hypertension (PH) was urgently operated upon. On follow-up, her PH worsened, resulting in right ventricular dysfunction and was later detected to have absent portal vein.

Left ventricular noncompaction in primary systemic carnitine deficiency: A rare association.

Left ventricular noncompaction (LVNC) is a rare phenotype of dilated cardiomyopathy. We report a child with primary systemic carnitine deficiency having associated LVNC.