Altered Cortical Activation Patterns in the Motor Cortex Post ACL Reconstruction Compared to Healthy Control

Following anterior cruciate ligament reconstruction (ACLR), patients often experience persistent knee dysfunction, such as knee strength deficit, possibly correlated with altered cortical activation in the brain. However, it remains unclear if ACLR patients exhibit different cortical activation patterns in the primary motor cortex (M1) during strength tasks, when compared to healthy control. PURPOSE: To examine electrocortical activation patterns in the M1 during submaximal isometric contraction of the quadriceps between an ACLR patient and a healthy control. METHODS: Both ACLR (female, 21yrs,180.34cm, 77.11kg) and control (female, 39yrs, 160.02cm, 61.23kg) performed isometric extension of the reconstructed or matched knees at 10% of their maximal voluntary isometric contraction (MVIC). Electrocortical activation was measured using a 64-channel mobile electroencephalograph (EEG) in response to 30 trials of unanticipated Transcranial Magnetic Stimulation (TMS) over the hotspot, a specific M1 location producing the largest amount of quadriceps activation. TMS were delivered at 120% (AMT 120) and 140% (AMT 140) of the active motor threshold (AMT), the minimum TMS intensity to induce measurable muscle twitch. Averaged event-related potential (ERP) was used to compare presence of positive (P40, P80, P200) and negative (N20, N60, N100) peaks from the onset of TMS between subjects. RESULTS: For AMT 120 the ACLR had ERP peaks at N20, P40, and P200 whereas the control had peaks at P80 and N100. For AMT 140 the ACLR had peaks at N20, P40, N60, and P80 whereas the control had peaks at N20, P80 and N100. CONCLUSION: Our preliminary data demonstrates that early ERP peaks in ACLR compared to the control may indicate altered neural processing at the M1, with greater differences at AMT120. Such neuroadaptation over the M1 in the ACLR may result in improper regulation of muscle contraction, leading to permanent strength deficit. Future studies are warranted to determine how the altered brain’s function affects the knee function in ACLR patients to enhance rehabilitation programs after ACLR

Nonlinear damping in mechanical resonators based on graphene and carbon nanotubes

Carbon nanotubes and graphene allow fabricating outstanding nanomechanical resonators. They hold promise for various scientific and technological applications, including sensing of mass, force, and charge, as well as the study of quantum phenomena at the mesoscopic scale. Here, we have discovered that the dynamics of nanotube and graphene resonators is in fact highly exotic. We propose an unprecedented scenario where mechanical dissipation is entirely determined by nonlinear damping. As a striking consequence, the quality factor Q strongly depends on the amplitude of the motion. This scenario is radically different from that of other resonators, whose dissipation is dominated by a linear damping term. We believe that the difference stems from the reduced dimensionality of carbon nanotubes and graphene. Besides, we exploit the nonlinear nature of the damping to improve the figure of merit of nanotube/graphene resonators.Comment: main text with 4 figures, supplementary informatio

다변량 기법을 이용한 혼합치열기 분석법

Objective: To develop a mixed dentition analysis method in consideration of the normal variation of tooth sizes. Methods: According to the tooth-size of the maxillary central incisor, maxillary 1st molar, mandibular central incisor, mandibular lateral incisor, and mandibular 1st molar, 307 normal occlusion subjects were clustered into the smaller and larger tooth-size groups. Multiple regression analyses were then performed to predict the sizes of the canine and premolars; for the 2 groups and both genders separately. For a cross validation dataset, 504 malocclusion patients were assigned into the 2 groups. Then multiple regression equations were applied. Results: Our results show that the maximum errors of the predicted space for the canine, 1st and 2nd premolars were 0.71 and 0.82 mm residual standard deviation for the normal occlusion and malocclusion groups, respectively. For malocclusion patients, the prediction errors did not imply a statistically significant difference depending on the types of malocclusion nor the types of tooth-size groups. The frequency of prediction error more than 1 mm and 2 mm were 17.3% and 1.8%, respectively. The overall prediction accuracy was dramatically improved in this study compared to that of previous studies. Conclusions: The computer aided calculation method used in this study appeared to be more efficient. (Korean J Orthod 2009;39(2):112-119)본 연구는 서울대학교 치과병원 연구비(04-2007-0013) 지원을 받아 시행되었음.

Marginal Zone B-cell Lymphoma of MALT in Small Intestine Associated with Amyloidosis: A Rare Association

A 62-yr-old man presented with a 5-yr history of intermittent abdominal distention and pain. These symptoms persisted for several months and subsided without treatment. A diagnosis of suspected small bowel lymphoma was made based on plain radiograph and computerized tomogram findings, and he was referred to our institution for further evaluation. Segmental resection of the small intestine was performed and the diagnosis of marginal zone B-cell lymphoma associated with amyloidosis was made. This is the first case of marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) in the small intestine associated with amyloidosis in Korea

Unusual Location of the Geotail Magnetopause Near Lunar Orbit: A Case Study

The Earth's magnetopause is highly variable in location and shape and is modulated by solar wind conditions. On 8 March 2012, the ARTEMIS probes were located near the tail current sheet when an interplanetary shock arrived under northward interplanetary magnetic field conditions and recorded an abrupt tail compression at ∼(‐60, 0, ‐5) RE in Geocentric Solar Ecliptic coordinate in the deep magnetotail. Approximately 10 minutes later, the probes crossed the magnetopause many times within an hour after the oblique interplanetary shock passed by. The solar wind velocity vector downstream from the shock was not directed along the Sun‐Earth line but had a significant Y component. We propose that the compressed tail was pushed aside by the appreciable solar wind flow in the Y direction. Using a virtual spacecraft in a global magnetohydrodynamic (MHD) simulation, we reproduce the sequence of magnetopause crossings in the X‐Y plane observed by ARTEMIS under oblique shock conditions, demonstrating that the compressed magnetopause is sharply deflected at lunar distances in response to the shock and solar wind VY effects. The results from two different global MHD simulations show that the shocked magnetotail at lunar distances is mainly controlled by the solar wind direction with a timescale of about a quarter hour, which appears to be consistent with the windsock effect. The results also provide some references for investigating interactions between the solar wind/magnetosheath and lunar nearside surface during full moon time intervals, which should not happen in general

A direct examination of the dynamics of dipolarization fronts using MMS

Energy conversion on the dipolarization fronts (DFs) has attracted much research attention through the suggestion that intense current densities associated with DFs can modify the more global magnetotail current system. The current structures associated with a DF are at the scale of one to a few ion gyroradii, and their duration is comparable to a spacecraft's spin period. Hence, it is crucial to understand the physical mechanisms of DFs with measurements at a timescale shorter than a spin period. We present a case study whereby we use measurements from the Magnetospheric Multiscale (MMS) Mission, which provides full 3-D particle distributions with a cadence much shorter than a spin period. We provide a cross validation amongst the current density calculations and examine the assumptions that have been adopted in previous literature using the advantages of MMS mission (i.e., small-scale tetrahedron and high temporal resolution). We also provide a cross validation on the terms in the generalized Ohm's law using these advantageous measurements. Our results clearly show that the majority of the currents on the DF are contributed by both ion and electron diamagnetic drifts. Our analysis also implies that the ion frozen-in condition does not hold on the DF, while electron frozen-in condition likely holds. The new experimental capabilities allow us to accurately calculate Joule heating within the DF, which shows that plasma energy is being converted to magnetic energy in our event

Substructures within a dipolarization front revealed by high-temporal resolution Cluster observations

The dipolarization front (DF), usually observed near the leading edge of a bursty bulk flow (BBF), is thought to carry an intense current sufficient to modify the large‐scale near‐Earth magnetotail current system. However, the physical mechanism of the current generation associated with DFs is poorly understood. This is primarily due to the limitations of conventional plasma instruments which are unable to provide a sufficient number of unaliased 3‐D distribution functions on the timescale of the DF, which usually travels past a spacecraft in only a few seconds. It is thus almost impossible to unambiguously determine the detailed plasma structure of the DF at the usual temporal resolution of such instruments. Here we present detailed plasma measurements using the Cluster Plasma Electron and Current Experiment and Cluster Ion Spectrometry‐Composition and Distribution Function ion data for an event during which it was possible to observe the full pitch angle distribution at a cadence of 1/4 s. The observations clearly show details of plasma substructure within the DF, including the presence of field‐aligned electron beams. In this event, the current density carried by the electron beam is much larger than the current obtained from the curlometer method. We also suggest that the field‐aligned current around the DF obtained from the curlometer method may have been misinterpreted in previous studies. Our results imply that the nature of the DF current system needs to be revisited using high‐resolution particle measurements, such as those observations shortly to be available from the Magnetospheric Multiscale mission

Ordering and the micromechanics of Ti-7Al

The evolution of intergranular lattice strain in the α titanium alloy Ti–7Al wt% was characterised using in situ time-of-flight (TOF) neutron diffraction during room temperature tensile loading. Samples were aged to promote ordering and the formation of nanometre-scale α2 (Ti3Al). On ageing, at 550°C and 625°C, dislocations were observed to travel in pairs, and in planar arrays, which has been attributed to the presence of ordering. A slight change in c/a was observed, from 1.6949 to 1.6945, and a slight increase in the macroscopic modulus. However, no changes were observed in the residual lattice strains, which are the grain-orientation average elastic strains produced by plasticity. Therefore it is inferred that the changes in deformation mechanisms caused by ordering that result in an enhanced vulnerability to dwell fatigue affect primarily the extent of slip localisation. The overall strain distributions between grains in different orientations are not changed