Hydrodynamics of the Developing Region in Hydrophobic Microchannels: A Dissipative Particle Dynamics Study

Dissipative Particle Dynamics (DPD) is becoming a popular particle based method to study flow through microchannels due to the ease with which the presence of biological cells or DNA chains can be modeled. Many Lab-On-Chip (LOC) devices require the ability to manipulate the transport of cells or DNA chains in the fluid flow. Microchannel surfaces coated with combinations of hydrophilic and hydrophobic materials have been found useful for this purpose. In this work, we have numerically studied the hydrodynamics of a steady nonuniform developing flow between two infinite parallel plates with hydrophilic and hydrophobic surfaces using DPD for the first time. The hydrophobic and hydrophilic surfaces were modeled using partial-slip and no-slip boundary conditions respectively in the simulations. We also propose a new method to model the inflow and outflow boundaries for the DPD simulations. The simulation results of the developing flow match analytical solutions from continuum theory for no-slip and partial-slip surfaces to good accord. The entrance region constitutes a considerable fraction of the channel length in miniaturized devices. Thus it is desirable for the length of the developing region to be short as most microfluidic devices such as cell or DNA separators and mixers are designed for the developed flow field. We studied the effect of a hydrophilic strip near the inlet of a microchannel on the effective developing length. We find that the presence of the hydrophobic strip significantly reduces the developing length

Clinical Correlates of High Cervical Fractional Anisotropy in Acute Cervical Spinal Cord Injury

Objective: Fractional anisotropy (FA) of the high cervical cord (C1-C2), rostral to the injury site, correlates with upper limb function in patients with chronic cervical spinal cord injury (SCI). In acute cervical SCI, this relationship has not been investigated. The objective of this study was to identify functional correlates of FA of the high cervical cord in a series of patients with acute cervical SCI. Methods: Traumatic cervical SCI patients who underwent presurgical cervical spine diffusion tensor imaging at our institution were reviewed for this study. FA of the whole cord as well as the lateralcorticospinal tracts (CSTs) was calculated on axial images from C1-C2. Upper limb motor (C5-T1) and sensory (C2-T1) function scores were extracted from the admission American Spinal Injury Association (ASIA) examinations. Correlation analysis for FA with ASIA examinations was performed using a Pearson correlation. Results: Twelve subjects (9 men, 3 women; mean age 54.7 ± 4.0 years) underwent cervical spine diffusion tensor imaging at a mean duration of 3.6 ± 0.9 days postinjury. No patient had cord compression or intramedullary T2-weighted hyperintensities within the C1-C2 segments. FA correlated with upper limb motor score (whole cord: r = 0.59, P = .04; CST: 0.67, P = .01) and the ASIA grade (whole cord: r = 0.61, P = .03; CST: r = 0.71, P = .009). No correlation was found between FA and sensory scores. Conclusions: FA of the whole cervical cord as well as the CST, rostral to the injury site, is associated with preserved upper limb motor function as well as superior ASIA grades after acute cervical SCI. FA of the high cervical cord is a potential biomarker of neural injury after acute cervical SCI

Context-aware Captions from Context-agnostic Supervision

We introduce an inference technique to produce discriminative context-aware image captions (captions that describe differences between images or visual concepts) using only generic context-agnostic training data (captions that describe a concept or an image in isolation). For example, given images and captions of "siamese cat" and "tiger cat", we generate language that describes the "siamese cat" in a way that distinguishes it from "tiger cat". Our key novelty is that we show how to do joint inference over a language model that is context-agnostic and a listener which distinguishes closely-related concepts. We first apply our technique to a justification task, namely to describe why an image contains a particular fine-grained category as opposed to another closely-related category of the CUB-200-2011 dataset. We then study discriminative image captioning to generate language that uniquely refers to one of two semantically-similar images in the COCO dataset. Evaluations with discriminative ground truth for justification and human studies for discriminative image captioning reveal that our approach outperforms baseline generative and speaker-listener approaches for discrimination.Comment: Accepted to CVPR 2017 (Spotlight

Diffusion Tensor Imaging Correlates with Short-Term Myelopathy Outcome in Patients with Cervical Spondylotic Myelopathy

Objective To determine if spinal cord diffusion tensor imaging indexes correlate with short-term clinical outcome in patients undergoing elective cervical spine surgery for cervical spondylotic myelopathy (CSM). Methods A prospective consecutive cohort study was performed in patients undergoing elective cervical spine surgery for CSM. After obtaining informed consent, patients with CSM underwent preoperative T2-weighted magnetic resonance imaging and diffusion tensor imaging of the cervical spine. Fractional anisotropy (FA) values at the level of maximum cord compression and at the noncompressed C1-2 level were calculated on axial images. We recorded the modified Japanese Orthopaedic Association (mJOA) scale, Neck Disability Index, and Short Form-36 physical functioning subscale scores for all patients preoperatively and 3 months postoperatively. Statistical analysis was performed to identify correlations between FA and clinical outcome scores. Results The study included 27 patients (mean age 54.5 years ± 1.9, 12 men). The mean postoperative changes in mJOA scale, Neck Disability Index, and Short Form-36 physical functioning subscale scores were 0.9 ± 0.3, −6.0 ± 1.9, and 3.4 ± 1.9. The mean FA at the level of maximum compression was significantly lower than the mean FA at the C1-2 level (0.5 vs. 0.55, P = 0.01). FA was significantly correlated with change in mJOA scale score (Pearson r = −0.42, P = 0.02). FA was significantly correlated with the preoperative mJOA scale score (Pearson r = 0.65, P \u3c 0.001). Conclusions Preoperative FA at the level of maximum cord compression significantly correlates with the 3-month change in mJOA scale score among patients with CSM. FA was also significantly associated with preoperative mJOA scale score and is a potential biomarker for spinal cord dysfunction in CSM

Severity of Spinal Cord Injury Influences Diffusion Tensor Imaging of the Brain

Background: The purpose of this study was to determine whether DTI changes in the brain induced by a thoracic spinal cord injury are sensitive to varying severity of spinal contusion in rats. Methods: A control, mild, moderate, or severe contusion injury was administered over the eighth thoracic vertebral level in 32 Sprague-Dawley rats. At 11 weeks postinjury, ex vivo DTI of the brain was performed on a 9.4T Bruker scanner using a pulsed gradient spin-echo sequence. Results: Mean water diffusion in the internal capsule regions of the brain and pyramid locations of the brainstem were correlated with motor function (r2 = 0.55). Additionally, there were significant differences between injury severity groups for mean diffusivity and fractional anisotropy at regions associated with the corticospinal tract (P = 0.05). Conclusion: These results indicate that DTI is sensitive to changes in brain tissue as a consequence of thoracic SCI