Highly Ordered Eutectic Mesostructures via Template-Directed Solidification within Thermally Engineered Templates.

Template-directed self-assembly of solidifying eutectics results in emergence of unique microstructures due to diffusion constraints and thermal gradients imposed by the template. Here, the importance of selecting the template material based on its conductivity to control heat transfer between the template and the solidifying eutectic, and thus the thermal gradients near the solidification front, is demonstrated. Simulations elucidate the relationship between the thermal properties of the eutectic and template and the resultant microstructure. The overarching finding is that templates with low thermal conductivities are generally advantageous for forming highly organized microstructures. When electrochemically porosified silicon pillars (thermal conductivity < 0.3 Wm-1K-1) are used as the template into which an AgCl-KCl eutectic is solidified, 99% of the unit cells in the solidified structure exhibit the same pattern. In contrast, when higher thermal conductivity crystalline silicon pillars (≈100 Wm-1K-1) are utilized, the expected pattern is only present in 50% of the unit cells. The thermally engineered template results in mesostructures with tunable optical properties and reflectances nearly identical to the simulated reflectances of perfect structures, indicating highly ordered patterns are formed over large areas. This work highlights the importance of controlling heat flows in template-directed self-assembly of eutectics.

Cellular Thermometry Considerations for Probing Biochemical Pathways.

Temperature is a fundamental thermodynamic property that can serve as a probe of biochemical reactions. Extracellular thermometry has previously been used to probe cancer metabolism and thermoregulation, with measured temperature changes of ~1-2 K in tissues, consistent with theoretical predictions. In contrast, previous intracellular thermometry studies remain disputed due to reports of >1 K intracellular temperature rises over 5 min or more that are inconsistent with theory. Thus, the origins of such anomalous temperature rises remain unclear. An improved quantitative understanding of intracellular thermometry is necessary to provide a clearer perspective for future measurements. Here, we develop a generalizable framework for modeling cellular heat diffusion over a range of subcellular-to-tissue length scales. Our model shows that local intracellular temperature changes reach measurable limits (>0.1 K) only when exogenously stimulated. On the other hand, extracellular temperatures can be measurable (>0.1 K) in tissues even from endogenous biochemical pathways. Using these insights, we provide a comprehensive approach to choosing an appropriate cellular thermometry technique by analyzing thermogenic reactions of different heat rates and time constants across length scales ranging from subcellular to tissues. Our work provides clarity on cellular heat diffusion modeling and on the required thermometry approach for probing thermogenic biochemical pathways.

Design and analysis of magnetostrictive sensors for wireless temperature sensing.

Magnetostrictive transducers are commonly used as actuators and sonar transducers, and in remote non-destructive evaluation. Their use in wireless thermometry is relatively unexplored. Since magnetostriction-based sensors are passive, they could potentially enable long-term near-field thermometry. While the temperature sensitivity of resonance frequency in magnetostrictive transducers has been reported in previous studies, the origin of the temperature sensitivity has, however, not been elucidated. Here, we identify material properties that determine temperature sensitivity and identify ways to improve sensitivity as well as the detection technique. Using a combination of analytical and computational methods, we systematically identify the material properties that directly influence the temperature coefficient of resonance frequency (TCF). We first experimentally measure the shift in resonance frequency due to temperature changes in a Metglas strip to be 0.03% K-1. Using insights from theory, we then experimentally demonstrate a fivefold improvement to the TCF by using Terfenol in place of Metglas as the magnetostrictive sensor material. We further demonstrate an alternate temperature sensing technique that does not require measuring the resonance frequency, consequently reducing instrument complexity. This work provides a general framework to analyze magnetostrictive materials and the sensing scheme for near-field wireless thermometry.

Multi-objective optimization of peel and shear strengths in ultrasonic metal welding using machine learning-based response surface methodology.

Ultrasonic metal welding (UMW) is a solid-state joining technique with varied industrial applications. Despite of its numerous advantages, UMW has a relative narrow operating window and is sensitive to variations in process conditions. As such, it is imperative to quantitatively characterize the influence of welding parameters on the resulting joint quality. The quantification model can be subsequently used to optimize the parameters. Conventional response surface methodology (RSM) usually employs linear or polynomial models, which may not be able to capture the intricate, nonlin-ear input-output relationships in UMW. Furthermore, some UMW applications call for simultaneous optimization of multiple quality indices such as peel strength, shear strength, electrical conductivity, and thermal conductivity. To address these challenges, this paper develops a machine learning (ML)- based RSM to model the input-output relationships in UMW and jointly optimize two quality indices, namely, peel and shear strengths. The performance of various ML methods including spline regression, Gaussian process regression (GPR), support vector regression (SVR), and conventional polynomial re-gression models with different orders is compared. A case study using experimental data shows that GPR with radial basis function (RBF) kernel and SVR with RBF kernel achieve the best prediction accuracy. The obtained response surface models are then used to optimize a compound joint strength indicator that is defined as the average of normalized shear and peel strengths. In addition, the case study reveals different patterns in the response surfaces of shear and peel strengths, which has not been systematically studied in the literature. While developed for the UMW application, the method can be extended to other manufacturing processes.

Intrinsic thermal interfacial resistance measurement in bonded metal-polymer foils.

Heat conduction through bonded metal-polymer interfaces often limits the overall heat transfer in electronic packaging, batteries, and heat recovery systems. To design the thermal circuit in such systems, it is essential to measure the thermal interfacial resistance (TIR) across ∼1 µm to 100 µm junctions. Previously reported TIR of metal-polymer junctions utilize ASTM E1530-based two-block systems that measure the TIR by applying pressure across the interface through external heating and cooling blocks. Here, we report a novel modification of the ASTM-E1530 technique that employs integrated heaters and sensors to provide an intrinsic TIR measurement of an adhesively bonded metal-polymer junction. We design the measurement technique using finite element simulations to either passively suppress or actively compensate the lateral heat diffusion through the polymer, which can minimize the systematic error to ≲5%. Through proof-of-concept experiments, we report the TIR of metal-polymer interfaces made from DuPont's Pyralux double-side copper-clad laminates, commonly used in flexible printed circuit boards. Our TIR measurement errors are <10%. We highlight additional sources of errors due to non-idealities in the experiment and discuss possible ways to overcome them. Our measurement technique is also applicable to interfaces that are electrically insulating such as adhesively joined metal-metal junctions and sputter-coated or welded metal-polymer junctions. Overall, the technique is capable of measuring TIR ≳10-5 m2 KW-1 in bonded metal-polymer foils and can be tailored for in situ measurements in flexible electronics, circuit packaging, and other hybrid metal-polymer systems.

Extreme Antiscaling Performance of Slippery Omniphobic Covalently Attached Liquids.

Scale formation presents an enormous cost to the global economy. Classical nucleation theory dictates that to reduce the heterogeneous nucleation of scale, the surface should have low surface energy and be as smooth as possible. Past approaches have focused on lowering surface energy via the use of hydrophobic coatings and have created atomically smooth interfaces to eliminate nucleation sites, or both, via the infusion of low-surface-energy lubricants into rough superhydrophobic substrates. Although lubricant-based surfaces are promising candidates for antiscaling, lubricant drainage inhibits their utilization. Here, we develop methodologies to deposit slippery omniphobic covalently attached liquids (SOCAL) on arbitrary substrates. Similar to lubricant-based surfaces, SOCAL has ultralow roughness and surface energy, enabling low nucleation rates and eliminating the need to replenish the lubricant. To enable SOCAL coating on metals, we investigated the surface chemistry required to ensure high-quality functionalization as measured by ultralow contact angle hysteresis (<3°). Using a multilayer deposition approach, we first electrophoretically deposit (EPD) silicon dioxide (SiO2) as an intermediate layer between the metallic substrate and SOCAL. The necessity of EPD SiO2 is to smooth (<10 nm roughness) as well as to enable the proper surface chemistry for SOCAL bonding. To characterize antiscaling performance, we utilized calcium sulfate (CaSO4) scale tests, showing a 20× reduction in scale deposition rate than untreated metallic substrates. Descaling tests revealed that SOCAL dramatically decreases scale adhesion, resulting in rapid removal of scale buildup. Our work not only demonstrates a robust methodology for depositing antiscaling SOCAL coatings on metals but also develops design guidelines for the creation of antifouling coatings for alternate applications such as biofouling and high-temperature coking.

Estimation of leaf area index using PROSAIL based LUT inversion, MLRA-GPR and empirical models: Case study of tropical deciduous forest plantation, North India.

Forests play a vital role in biological cycles and environmental regulation. To understand the key processes of forest canopies (e.g., photosynthesis, respiration and transpiration), reliable and accurate information on spatial variability of Leaf Area Index (LAI), and its seasonal dynamics is essential. In the present study, we assessed the performance of biophysical parameter (LAI) retrieval methods viz. Look-Up Table (LUT)-inversion, MLRA-GPR (Machine Learning Regression Algorithm-Gaussian Processes Regression) and empirical models, for estimating the LAI of tropical deciduous plantation using ARTMO (Automated Radiative Transfer Models Operator) tool and Sentinel-2 satellite images. The study was conducted in Central Tarai Forest Division, Haldwani, located in the Uttarakhand state, India. A total of 49 ESUs (Elementary Sampling Unit) of 30m×30m size were established based on variability in composition and age of plantation stands. In-situ LAI was recorded using plant canopy imager during the leaf growing, peak and senescence seasons. The PROSAIL model was calibrated with site-specific biophysical and biochemical parameters before used to the predicted LAI. The plantation LAI was also predicted by an empirical approach using optimally chosen Sentinel-2 vegetation indices. In addition, Sentinel-2 and MODIS LAI products were evaluated with respect to LAI measurements. MLRA-GPR offered best results for predicting LAI of leaf growing (R2 = 0.9, RMSE = 0.14), peak (R2 = 0.87, RMSE = 0.21) and senescence (R2 = 0.86, RMSE = 0.31) seasons while LUT inverted model outperformed VI's based parametric regression model. Vegetation indices (VIs) derived from 740 nm, 783 nm and 2190 nm band combinations of Sentinel-2 offered the best prediction of LAI.

Transient heat release during induced mitochondrial proton uncoupling.

Non-shivering thermogenesis through mitochondrial proton uncoupling is one of the dominant thermoregulatory mechanisms crucial for normal cellular functions. The metabolic pathway for intracellular temperature rise has widely been considered as steady-state substrate oxidation. Here, we show that a transient proton motive force (pmf) dissipation is more dominant than steady-state substrate oxidation in stimulated thermogenesis. Using transient intracellular thermometry during stimulated proton uncoupling in neurons of Aplysia californica, we observe temperature spikes of ~7.5 K that decay over two time scales: a rapid decay of ~4.8 K over ~1 s followed by a slower decay over ~17 s. The rapid decay correlates well in time with transient electrical heating from proton transport across the mitochondrial inner membrane. Beyond ~33 s, we do not observe any heating from intracellular sources, including substrate oxidation and pmf dissipation. Our measurements demonstrate the utility of transient thermometry in better understanding the thermochemistry of mitochondrial metabolism.

Endovascular Occlusion of Cervical Internal Carotid Artery Pseudoaneurysm in a Child Treated by N-Butyl Cyanoacrylate: A Rare Case Report.

We report a rare case of spontaneous extracranial cervical internal carotid artery (ICA) pseudoaneurysm in a female child aged 3 years who presented with a swelling in the neck which had bled following an attempted incision as it had been thought to be an abscess. A CT angiogram and an MR angiogram were not very conclusive to diagnose the exact site of origin and the morphology of the aneurysm. Digital subtraction angiography revealed a dissecting pseudoaneurysm of the right extracranial cervical ICA. The right ICA was ending as a pseudosac, and the right cerebral circulation was filling up through the right posterior cerebral artery. To minimize the radiation exposure, a microcatheter was placed inside the diagnostic catheter. The aneurysm sac was occluded using N-butyl cyanoacrylate since there was no distal flow to the brain from the artery beyond the aneurysm. It was a safe, effective and cheaper alternative to open surgery or to other endovascular management options available. Not all neck swellings are abscesses, and they should be examined and evaluated to exclude a vascular cause.

Occiput/C1-C2 fixations using intra-laminar screw of axis - A long-term follow-up.

BACKGROUND: The surgical management of the craniocervical junction is challenging. Rigid posterior fixation of occiput/C1-C2 can be performed using a variety of surgical techniques including C2 pedicle/pars interarticularis, transarticular and intralaminar screw fixations. METHODS: Forty-one patients were treated with occipital plate/C1 lateral mass and C2 intra-laminar screw fixations for basilar invagination and congenital atlantoaxial subluxation, post-traumatic instability, tuberculous and rheumatoid arthritis-associated atlantoaxial dislocation. Out of forty-one, thirty-six patients had bilateral crossing intra-laminar screws and five had ipsilateral laminar screw fixation bilaterally. RESULTS: Follow-up was done in thirty-nine patients from 6 months to 8 years (mean: 21 months) and solid osseous fusion could be achieved in all (100%). One patient was lost to follow-up and another patient died of a cause unrelated to surgical technique. Pre-operative and post-operative Neurosurgical Cervical Spine Scale showed improvement in all patients having features of myelopathy. There were no neurological or vascular complications. However, nine patients had posterior laminar breach, eight had anterior laminar penetrations and three had wound infections. One patient had transient bulbar palsy and one patient had hardware failure in the form of avulsion of the midline occipital plate. CONCLUSIONS: Intra-laminar screw fixation is a safe alternative to transarticular and transpedicular/pars interarticularis fixation of C2 with advantage of having no risk of injury to vertebral artery and comparable biomechanical and pull-out strength.

Controllable doping and wrap-around contacts to electrolessly etched silicon nanowire arrays.

Top-down electroless chemical etching enables non-lithographic patterning of wafer-scale nanostructured arrays, but the etching on highly doped wafers produces porous structures. The lack of defect-free nanostructures at desired doping and the difficulties in forming reliable electrical side-contacts to the nanostructure arrays limits their integration into high performance nanoelectronics. We developed a barrier layer diffusion technique to controllably dope wafer-scale silicon nanowire arrays (10(17)-10(20) cm(-3)) produced by chemically etching lightly doped silicon wafers. In order to achieve low resistance top-side electrical contacts to the arrays, we developed a two step tip-doping procedure to locally dope the tips (∼10(20) cm(-3)) to metallic levels. The dopant concentration is characterized by depth profiling using secondary ion mass spectroscopy and four-point probe electrical measurements. Further, array scale electrical measurements show that the tip-doping lowers the specific contact resistivity (∼10(-5) Ω cm(2)) since the metallic tips enable direct tunneling of electrons across the nickel silicide contacts to the nanowire arrays. This work provides a scalable and cost-effective doping approach to control charge injection and charge conduction in nanowire arrays, thus advancing their integration into various device applications.

Rigid variety occiput/C1-C2-C3 internal fixation in pediatric population.

PURPOSE: The purpose of this study was to review our experience of rigid internal fixation of craniovertebral junction in pediatric population. A new technique of reduction of basilar invagination with atlantoaxial dislocation is described. To the best of our knowledge and available scientific literature, this technique has not yet been described in younger patients. METHODS: We have managed 27 children by rigid variety of occiput/C1-C2-C3 internal fixation of various craniovertebral junction pathologies. All patients were subjected to thin cuts of computed tomography with 3D reconstruction for selecting appropriate rigid construct. Eight children had occiput-C2, 3 had occiput-C2-C3, and 16 had C1-C2 hardware constuct. One patient of C1-C2-plate fixation had section of C2 nerve root ganglia. Basilar invagination with atlantoaxial dislocation was reduced by new distraction/compression techniques. RESULTS: Improvement in clinical features and correction of deformity with solid hardware construct were seen in all patients. Follow-up period ranged from 5-72 months. One patient was lost to follow-up, and one case died of compression of vertebral artery at C1 lateral mass. Patients of myelopathy had recovery rate of 90.9%. Hardware failure was seen in one patient, and wound infection was observed in two cases. CONCLUSIONS: Rigid variety of occiput/C1-C2 internal fixation is a safe and effective method in the management of variety of craniovertebral pathologies in pediatric population. This new technique of reduction of basilar invagination with atlantoaxilal dislocation from posterior approach may alleviate the need of high morbity associated with surgical procedure like transoral odontoidectomy in younger patients.

Coherent phonon-grain boundary scattering in silicon inverse opals.

We report measurements and modeling of thermal conductivity in periodic three-dimensional dielectric nanostructures, silicon inverse opals. Such structures represent a three-dimensional "phononic crystal" but affect heat flow instead of acoustics. Employing the Stober method, we fabricate high quality silica opal templates that on filling with amorphous silicon, etching and recrystallizing produce silicon inverse opals. The periodicities and shell thicknesses are in the range 420-900 and 18-38 nm, respectively. The thermal conductivity of inverse opal films are relatively low, ~0.6-1.4 W/mK at 300 K and arise due to macroscopic bending of heat flow lines in the structure. The corresponding material thermal conductivity is in the range 5-12 W/mK and has an anomalous ~T(1.8) dependence at low temperatures, distinct from the typical ~T(3) behavior of bulk polycrystalline silicon. Using phonon scattering theory, we show such dependence arising from coherent phonon reflections in the intergrain region. This is consistent with an unconfirmed theory proposed in 1955. The low thermal conductivity is significant for applications in photonics where they imply significant temperature rise at relatively low absorption and in thermoelectrics, where they suggest the possibility of enhancement in the figure of merit for polysilicon with optimal doping.

Porosity control in metal-assisted chemical etching of degenerately doped silicon nanowires.

We report the fabrication of degenerately doped silicon (Si) nanowires of different aspect ratios using a simple, low-cost and effective technique that involves metal-assisted chemical etching (MacEtch) combined with soft lithography or thermal dewetting metal patterning. We demonstrate sub-micron diameter Si nanowire arrays with aspect ratios as high as 180:1, and present the challenges in producing solid nanowires using MacEtch as the doping level increases in both p- and n-type Si. We report a systematic reduction in the porosity of these nanowires by adjusting the etching solution composition and temperature. We found that the porosity decreases from top to bottom along the axial direction and increases with etching time. With a MacEtch solution that has a high [HF]:[H(2)O(2)] ratio and low temperature, it is possible to form completely solid nanowires with aspect ratios of less than approximately 10:1. However, further etching to produce longer wires renders the top portion of the nanowires porous.

Bilateral open-door expansive laminoplasty using unilateral posterior midline approach with preservation of posterior supporting elements for management of cervical myelopathy and radiculomyelopathy--analysis of clinical and radiological outcome and surgical technique.

BACKGROUND: The purpose of this study was to evaluate bilateral open-door cervical laminoplasty for management of cervical canal stenosis secondary to multisegmental cervical spondylosis and ossified posterior longitudinal ligament. The importance of unilateral posterior approach with preservation of posterior supporting element is emphasized. METHODS: Thirty-four patients had expansive laminoplasty. Posterior tension band consisting of nuchal ligaments and supraspinous and interspinous ligaments was secured. Paraspinal deep extensor muscles attached to one side of spinous process were also preserved. Hydroxyapatite-collagen spacers were positioned between split laminae in midline and secured with Ethibond. All patients had features of myelopathy with weakness, hypertonia, clonus, and hyperreflexia in both upper and lower limbs. Bladder and bowel involvement was seen in 11.7% and sexual dysfunction in 5.8%. Preoperative dynamic study of cervical spine, MRI, and/or CT were done in all patients and compared with postoperative studies to see the efficacy of the surgical procedure. RESULTS: Preoperative and postoperative neurosurgical cervical spine scale was used to compare results in relation to age, sex, duration of symptoms, neurosurgical cervical spine score, bladder, bowel, and sexual abnormalities. Elderly patients, lower neurosurgical score, signs and symptoms of more than 2 years, and bladder, bowel, and sexual dysfunction had poorer outcome. Complications were few. All patients had adequate diameter of spinal canal postoperatively. Cervical alignment and range of motion of segment subjected to laminoplasty were preserved satisfactorily in follow-up. CONCLUSIONS: Bilateral open-door expansive laminoplasty using unilateral posterior midline approach provides preservation of posterior supporting tension band and excellent reconstruction of spinal canal. This technique also does not compromise contralateral paraspinal muscles attached to spinous process.

Progressive multifocal leukoencephalopathy in a patient with idiopathic CD4+T lymphocytopenia.

Progressive multifocal leukoencephalopathy (PML) is demyelinating of central nervous system caused by JC virus infection and often occurs in immunodeficient individuals. We report progressive PML in a 30-year-old male with idiopathic severely depressed CD4+T lymphocyte count. He was sero-negative for human immunodeficiency virus (HIV) infection.

Fatal epistaxis from the fetal posterior communicating artery--a delayed complication of trans-sphenoidal surgery.

Vascular complications following trans-sphenoidal surgery can occur due to injury of the cavernous segment of the internal carotid artery, external carotid artery and its branches or an aneurysm rupture. The incidence of vascular complications in trans-sphenoidal surgery is 0.4% to 1.4%. Vascular injury was encountered in a patient with giant pituitary adenoma who underwent staged trans-sphenoidal tumour removal. Following his third surgery, he had delayed fatal epistaxis. An angiogram revealed a fetal type posterior communicating artery with a blow out of the junction of the posterior communicating artery with the posterior cerebral artery. The diagnosis and management of this condition are discussed.