The Strain Movie 2014

[Nella Mcnairy]

Astrain is when a muscle is stretched too much and part of it tears. It is also called a pulled muscle. A strain is a painful injury. It can be caused by an accident, overusing a muscle, or using a muscle in the wrong way.

Updated by: Linda J. Vorvick, MD, Clinical Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

In mechanics, strain is defined as relative deformation, compared to a reference position configuration. Different equivalent choices may be made for the expression of a strain field depending on whether it is defined with respect to the initial or the final configuration of the body and on whether the metric tensor or its dual is considered.

Strain has dimension of a length ratio, with SI base units of meter per meter (m/m).Hence strains are dimensionless and are usually expressed as a decimal fraction or a percentage.Parts-per notation is also used, e.g., parts per million or parts per billion (sometimes called "microstrains" and "nanostrains", respectively), corresponding to μm/m and nm/m.

A strain is in general a tensor quantity. Physical insight into strains can be gained by observing that a given strain can be decomposed into normal and shear components. The amount of stretch or compression along material line elements or fibers is the normal strain, and the amount of distortion associated with the sliding of plane layers over each other is the shear strain, within a deforming body.[2] This could be applied by elongation, shortening, or volume changes, or angular distortion.[3]

The state of strain at a material point of a continuum body is defined as the totality of all the changes in length of material lines or fibers, the normal strain, which pass through that point and also the totality of all the changes in the angle between pairs of lines initially perpendicular to each other, the shear strain, radiating from this point. However, it is sufficient to know the normal and shear components of strain on a set of three mutually perpendicular directions.

If there is an increase in length of the material line, the normal strain is called tensile strain; otherwise, if there is reduction or compression in the length of the material line, it is called compressive strain.

In each of these theories the strain is then defined differently. The engineering strain is the most common definition applied to materials used in mechanical and structural engineering, which are subjected to very small deformations. On the other hand, for some materials, e.g., elastomers and polymers, subjected to large deformations, the engineering definition of strain is not applicable, e.g. typical engineering strains greater than 1%;[4] thus other more complex definitions of strain are required, such as stretch, logarithmic strain, Green strain, and Almansi strain.

The true shear strain is defined as the change in the angle (in radians) between two material line elements initially perpendicular to each other in the undeformed or initial configuration. The engineering shear strain is defined as the tangent of that angle, and is equal to the length of deformation at its maximum divided by the perpendicular length in the plane of force application, which sometimes makes it easier to calculate.

The stretch ratio is used in the analysis of materials that exhibit large deformations, such as elastomers, which can sustain stretch ratios of 3 or 4 before they fail. On the other hand, traditional engineering materials, such as concrete or steel, fail at much lower stretch ratios.

The (infinitesimal) strain tensor (symbol ε \displaystyle \boldsymbol \varepsilon ) is defined in the International System of Quantities (ISQ), more specifically in ISO 80000-4 (Mechanics), as a "tensor quantity representing the deformation of matter caused by stress. Strain tensor is symmetric and has three linear strain and three shear strain (Cartesian) components."[6]ISO 80000-4 further defines linear strain as the "quotient of change in length of an object and its length" and shear strain as the "quotient of parallel displacement of two surfaces of a layer and the thickness of the layer".[6]Thus, strains are classified as either normal or shear. A normal strain is perpendicular to the face of an element, and a shear strain is parallel to it. These definitions are consistent with those of normal stress and shear stress.

A strain field associated with a displacement is defined, at any point, by the change in length of the tangent vectors representing the speeds of arbitrarily parametrized curves passing through that point. A basic geometric result, due to Frchet, von Neumann and Jordan, states that, if the lengths of the tangent vectors fulfil the axioms of a norm and the parallelogram law, then the length of a vector is the square root of the value of the quadratic form associated, by the polarization formula, with a positive definite bilinear map called the metric tensor.

The difference between a strain and a sprain is that a strain involves an injury to a muscle or to the band of tissue that attaches a muscle to a bone, while a sprain injures the bands of tissue that connect two bones together.

Acute strains can be caused by one event, such as using poor body mechanics to lift something heavy. Chronic muscle strains can result from repetitive injuries when you stress a muscle by doing the same motion over and over.

Regular stretching and strengthening exercises for your sport, fitness or work activity, as part of an overall physical conditioning program, can help to minimize your risk of muscle strains. Try to be in shape to play your sport; don't play your sport to get in shape. If you have a physically demanding occupation, regular conditioning can help prevent injuries.

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The Berry curvature dipole is a physical quantity that is expected to allow various quantum geometrical phenomena in a range of solid-state systems. Monolayer transition metal dichalcogenides provide an exceptional platform to modulate and investigate the Berry curvature dipole through strain. Here, we theoretically demonstrate and experimentally verify for monolayer MoS2 the generation of valley orbital magnetization as a response to an in-plane electric field due to the Berry curvature dipole. The measured valley orbital magnetization shows excellent agreement with the calculated Berry curvature dipole, which can be controlled by the magnitude and direction of strain. Our results show that the Berry curvature dipole acts as an effective magnetic field in current-carrying systems, providing a novel route to generate magnetization.

Valley magnetization measurement on a monolayer MoS2. (a) PL with increasing strain. Inset: Strain dependence of the PL center wavelength (λc). (b) I-V curve of the MoS2 channel at zero strain. Inset: Channel conductance as a function of strain. (c) θKR measured at the center of the MoS2 channel as a function of bias voltage (Vds) with increasing strain. (d) Strain dependence of θKR normalized by the channel current density (J).

Experimental and theoretical Berry curvature dipoles (D) and normalized valley magnetizations (M/J). (a) D and M/J measured from five different devices. For devices A and B, both strain and E are applied along x^zigzag. For devices C and D, strain is applied along y^armchair and E is applied along x^zigzag. For device E, strain is applied along x^zigzag and E is applied along y^armchair. (b) Calculated D and M/J when strain is applied along x^zigzag (red circles) and y^armchair (blue triangles).

Make a conscious effort to blink as often as possible. This keeps the surface of your eyes from drying out. You might even want to put a sticky note on your computer screen reminding you to blink often!

If your screen glows brighter than your surroundings, your eyes have to work harder to see. Adjust your screen brightness to match the level of light around you. Also, try increasing the contrast on your screen to reduce eye strain.

Do you find watching 3-D movies makes your eyes very tired? Or do you experience headaches or feel dizzy when gaming using a virtual reality (VR) headset? You may have a problem with focusing or depth perception.

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You can get these injuries to any muscle in your body if you push it beyond its normal limit, whether you're doing regular daily activities like lifting something heavy, working out, or playing sports. Back, calf, and hamstring strains are among the most common types of muscle strains.

Grade 2 muscle strain: While this is more serious than a grade 1 muscle strain, your muscle hasn't completely torn. Still, you'll have less strength and motion in that muscle, and maybe some swelling and bruising. It may take 2-3 months to recover.

Grade 3 muscle strain: This is a serious injury where your muscle tears into two pieces or shears away from the tendon. You won't be able to use the muscle and will have significant pain, swelling, and bruising. This type of injury might need to be repaired with surgery.

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