Interaponeurosis shear strain modulates behavior of myotendinous junction of the human triceps surae.

Muscle fascicles insert into a sheet-like aponeurosis. Adjacent aponeuroses are structurally in contact with each other, and ultimately merge into a common tendon. Consequently, fascicle shortening in planes of tissue layers in adjacent compartments must cause sliding between aponeuroses parallel to the acting forces. In this study, we used velocity-encoded, phase-contrast, and water-saturated spin-lattice relaxation time-weighted imaging to identify and track fascicle and aponeurosis behaviors of human medial gastrocnemius (MG) and soleus (Sol) during 15° dorsiflexion to 30° plantarflexion contractions of the ankle. Interaponeurosis shear strain, which was defined as the relative displacement of the aponeurosis at the fascicle end points (insertion) of the MG and Sol, was an average of 1.35 ± 0.27% (range 1.12 ∼ 1.87%), indicating that the strain is greater in the aponeurosis of MG fascicle insertion than the Sol. The myotendinous junction (MTJ) displacement increased significantly with decreasing interaponeurosis shear strain (P < 0.05). The magnitude of interaponeurosis shear strain had significant correlation with the temporal difference between the time at which the peak aponeurosis displacement of the MG and Sol occurred (P < 0.05). Our model also indicated that theoretical MTJ displacement varies in relation to temporal difference: no temporal difference caused the largest MTJ displacement and presence of temporal differences indicated a reduction in MTJ displacement. Therefore, we concluded that interaponeurosis shear strain is a mechanism enabling individual muscle contraction and thus specific loading of the tendon and joint

Microstructural analysis of skeletal muscle force generation during aging.

Human aging results in a progressive decline in the active force generation capability of skeletal muscle. While many factors related to the changes of morphological and structural properties in muscle fibers and the extracellular matrix (ECM) have been considered as possible reasons for causing age-related force reduction, it is still not fully understood why the decrease in force generation under eccentric contraction (lengthening) is much less than that under concentric contraction (shortening). Biomechanically, it was observed that connective tissues (endomysium) stiffen as ages, and the volume ratio of connective tissues exhibits an age-related increase. However, limited skeletal muscle models take into account the microstructural characteristics as well as the volume fraction of tissue material. This study aims to provide a numerical investigation in which the muscle fibers and the ECM are explicitly represented to allow quantitative assessment of the age-related force reduction mechanism. To this end, a fiber-level honeycomb-like microstructure is constructed and modeled by a pixel-based Reproducing Kernel Particle Method (RKPM), which allows modeling of smooth transition in biomaterial properties across material interfaces. The numerical investigation reveals that the increased stiffness of the passive materials of muscle tissue reduces the force generation capability under concentric contraction while maintains the force generation capability under eccentric contraction. The proposed RKPM microscopic model provides effective means for the cellular-scale numerical investigation of skeletal muscle physiology. NOVELTY STATEMENT: A cellular-scale honeycomb-like microstructural muscle model constructed from a histological cross-sectional image of muscle is employed to study the causal relations between age-associated microstructural changes and age-related force loss using Reproducing Kernel Particle Method (RKPM). The employed RKPM offers an effective means for modeling biological materials based on pixel points in the medical images and allow modeling of smooth transition in the material properties across interfaces. The proposed microstructure-informed muscle model enables quantitative evaluation on how cellular-scale compositions contribute to muscle functionality and explain differences in age-related force changes during concentric, isometric and eccentric contractions

Investigating the Correlation between Force Output, Strains, and Pressure for Active Skeletal Muscle Contractions

Experimental observations suggest that the force output of the skeletal muscle tissue can be correlated to the intra-muscular pressure generated by the muscle belly. However, pressure often proves difficult to measure through in-vivo tests. Simulations on the other hand, offer a tool to model muscle contractions and analyze the relationship between muscle force generation and deformations as well as pressure outputs, enabling us to gain insight into correlations among experimentally measurable quantities such as principal and volumetric strains, and the force output. In this work, a correlation study is performed using Pearson's and Spearman's correlation coefficients on the force output of the skeletal muscle, the principal and volumetric strains experienced by the muscle and the pressure developed within the muscle belly as the muscle tissue undergoes isometric contractions due to varying activation profiles. The study reveals strong correlations between force output and the strains at all locations of the belly, irrespective of the type of activation profile used. This observation enables estimation on the contribution of various muscle groups to the total force by the experimentally measurable principal and volumetric strains in the muscle belly. It is also observed that pressure does not correlate well with force output due to stress relaxation near the boundary of muscle belly

Small population face recognition for a kiosk interface

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaves 54-56).by Shantanu Kumar Sinha.M.Eng

Connectivity of the Superficial Muscles of the Human Perineum: A Diffusion Tensor Imaging-Based Global Tractography Study.

Despite the importance of pelvic floor muscles, significant controversy still exists about the true structural details of these muscles. We provide an objective analysis of the architecture and orientation of the superficial muscles of the perineum using a novel approach. Magnetic Resonance Diffusion Tensor Images (MR-DTI) were acquired in 10 healthy asymptomatic nulliparous women, and 4 healthy males. Global tractography was then used to generate the architecture of the muscles. Micro-CT imaging of a male cadaver was performed for validation of the fiber tracking results. Results show that muscles fibers of the external anal sphincter, from the right and left side, cross midline in the region of the perineal body to continue as transverse perinea and bulbospongiosus muscles of the opposite side. The morphology of the external anal sphincter resembles that of the number '8' or a "purse string". The crossing of muscle fascicles in the perineal body was supported by micro-CT imaging in the male subject. The superficial muscles of the perineum, and external anal sphincter are frequently damaged during child birth related injuries to the pelvic floor; we propose the use of MR-DTI based global tractography as a non-invasive imaging technique to assess damage to these muscles

NEGATIVE STRAIN IN THE SOLEUS POSTERIOR APONEUROSIS DURING HUMAN VOLUNTARY ISOMETRIC CONTRACTION

Aponeurosis in a pennate muscle has been modelled as an in-series structure (3) with homogeneous elasticity along the length of the muscle. Therefore, one can readily assume that muscle and aponeurosis sustain forces in the same proportion and thus, aponeurosis strain (L/L0) is homogeneous. This study aimed to investigate force-elongation (strain) characteristics of aponeurosis in in-vivo human soleus during voluntary contraction

Beyond SynFloods: Guarding Web Server Resources from DDoS Attacks

Problem. Denial-of-Service attacks on web servers take many forms. In this paper, we look at a new breed of application-level attacks. An attacker compromises a large number of dummy clients (by means of a worm, virus or Trojan horse) and causes the clients to flood the web server with well-formed HTTP requests that download large files or generate complex database queries. Such requests cause the web server to expend costly server resources like sockets, disk bandwidth, database sub-system bandwidth and worker processes on these dummy users. As a result, performance seen by legitimate users will degrade, eventually leading to denial of service. These attacks are hard to counter as the malicious requests are indistinguishable from legitimate requests at the server. Further, the dummy requests arrive from a large number of geographically distributed machines; thus, they cannot be filtered on source IP addresses or arrival patterns. Prior work has looked at network/transport level DDoS attacks such as SYN flood and bandwidth attacks Approach. Despite the distributed nature of clients participating in a DDoS attack, typically a small group of human operators initiates and manages the attack. By requiring the clients to interact with their human operator before they access server resources, we limit the speed of the DDoS attack and make the human attacker a shared bottleneck. In our system, a web-server can be in either of two modes, NOR-MAL and UNDER ATTACK. The server behavior is unchanged in NORMAL mode. When the web server perceives resource depletion beyond an acceptable limit it shifts to the UNDER ATTACK mode. In this mode, the server continues to serve connections that were established during the NORMAL mode. The server asks new clients to solve a puzzle that is easy to solve by a human but difficult to compute by a machine, before providing access to the system. Depending upon the desired level of protection, the puzzle could be a variation on the following text: "We are suspecting a DDoS attack on Foo. To access Foo, type in the text box à after replacing the number 6 by 2" or a URL embedded in an image -a CAPTCHA One concern is that the user might not be willing to solve the puzzle. In this case, our system behaves like current systems which handle these attacks by asking the user to "come back later". The user can still choose to ignore the puzzle and "come back later"; solving the puzzle enables the user immediate access to the server. Challenges. Incorporating a human in the loop has been used to counter automated user account creation and e-mail spam. However, using this approach to prevent a DDoS attack on web server resources is different due to the following challenges. 1. The puzzle should be sent and validated without allocating any TCB's or sockets at the server, while ensuring correct TCP congestion control semantics. 2. The client's TCP stack and the browser should not be modified. 3. Mechanism should be transparent to web caches. 4. A normal user would have to manually enter the key just once per browsing session, potentially consisting of multiple TCP connections. 5. If the system is experiencing a flash crowd rather than a DDoS attack, the mechanism should be benign. 6. Validation should be independent of the source IP address as malicious users could share IP with ordinary users due to NAT or spoofing. 7. One puzzle allows access to only one client, so it is useless for an attacker to solve a puzzle and distribute it to a large number of worms. 8. Switching from NORMAL to UNDER ATTACK mode (and vice versa) should be inexpensive and transparent to ongoing sessions. 9. Mechanism should work when requests are handled by a server farm. Ongoing Implementation. We are working on an implementation running Apache on Linux to address the above challenges -some aspects of which are discussed below. Currently, we use CAPTCHAlike images(1-2 pkts) as puzzles but are experimenting with natural language puzzles which are smaller in size. The puzzle is returned in an HTML form. To solve the puzzle, a human user types the answer(key) and submits the form creating an HTTP request containing GET /validate?answer=KEY . On a new connection request (i.e. SYNs to the web server), we want to send a puzzle and validate the key without allocating any TCB's or sockets at the server. The server responds to SYN packets with a SYN Cookie. The client receives the SYN cookie, increases its congestion window to two packets, transmits a SYNACKACK and the first data packet that usually contains the HTTP request. The kernel at the server end does not create a new socket upon completion of the TCP handshake. Instead the SYNACK-ACK packet is discarded. When the server receives the client's data packet, if the header of the HTTP request is not of the form GET /validate?answer=KEY , then this packet begins an HTTP session and is not an attempt at validating a key. The server replies with a new puzzle (1-2 pkts) as the HTTP response and immediately resets the connection (using the TCP RST flag). Otherwise, the kernel checks the cryptographic validity of the key. If the check succeeds, a socket is established and the request is delivered to the application. Note that this scheme preserves TCP congestion control semantics and prevents attacks that hog TCB's and sockets by establishing connections that exchange no data. The above scheme creates the following per-session overhead when the server is in UNDER ATTACK mode; two hashes to validate the answer, a few memory accesses to look at HTTP headers, fetching a puzzle and sending it to the client. To ensure that a user needs to solve a puzzle once even if the session contains multiple HTTP 1.0 connnections, the server uses a cookie at the client. Again note that the attacker cannot mount an attack by replicating a cookie because each cookie is mapped to a single key and the server constrains the number of connections using the same key to be small (e.g. four). Assuming that worms are not equipped with OCR software or natural language parsers, the rate at which malicious clients gain access is equal to the rate at which the human operators solve puzzles. To prevent attackers from distributing one puzzle's answer to a herd of clients, the server constrains the number of active TCP connections per key

Strain Anisotropy Driven Spontaneous Formation of Nanoscrolls from Two-Dimensional Janus Layers

Two-dimensional Janus transition metal dichalcogenides (TMDs) have attracted attention due to their emergent properties arising from broken mirror symmetry and self-driven polarisation fields. While it has been proposed that their vdW superlattices hold the key to achieving superior properties in piezoelectricity and photovoltiacs, available synthesis has ultimately limited their realisation. Here, we report the first packed vdW nanoscrolls made from Janus TMDs through a simple one-drop solution technique. Our results, including ab-initio simulations, show that the Bohr radius difference between the top sulphur and the bottom selenium atoms within Janus M_Se^S (M=Mo, W) results in a permanent compressive surface strain that acts as a nanoscroll formation catalyst after small liquid interaction. Unlike classical 2D layers, the surface strain in Janus TMDs can be engineered from compressive to tensile by placing larger Bohr radius atoms on top (M_S^Se) to yield inverted C scrolls. Detailed microscopy studies offer the first insights into their morphology and readily formed Moir\'e lattices. In contrast, spectroscopy and FETs studies establish their excitonic and device properties and highlight significant differences compared to 2D flat Janus TMDs. These results introduce the first polar Janus TMD nanoscrolls and introduce inherent strain-driven scrolling dynamics as a catalyst to create superlattices