biomechanics final mc/short answer questions

describe two limitations of using AFM to approximate the local mechanical properties of a single cell:

- mechanical properties change depending on where in the cell you're testing - not exact, assume linear deflection

the minimum number of markers to be embedded in a specimen to quantify the strain in 3-D is

4

when a cylindrical specimen is subjected to a torsional load, the maximum tensile stress is generated in the direction that is...

45 degrees to the long axis

in 3-D, there are 9 components of stress relative to the prescribed coordinate system. of which, how many components are independent?

6

in Hooke's law, how many independent parameters (E, G, etc.) are needed to completely describe orthotropic behavior (normal and shear) under isothermal conditions?

9

given the following AFM cantilever tip geometries, rank each tip by the amount of applied force it would take in order to achieve the same level of indentation (least force to most force):

A < C < B

in order to calculate stresses in a circular shat subjected to torsion, one must know:

applied torque, radius of the shaft, geometry of cross-section to calculate second polar moment of area

a condition characterized by hardening and narrowing of the artery from plaque buildup is known as ____.

atherosclerosis

shear strain is a measure of:

average change in the angle of distortion on xy-plane

hypertension significantly increases the risk of:

b & c: heart attack & kidney disease

with quantitative clinical gait analysis, conventional video recording is not important because of the captured motion data.

false

"clearance in gait" refers to what quantity/parameter?

foot height during swing phase

the gait event that marks the end of stance phase and beginning of swing phase is called what?

foot off

list two application area where motion capture technology is used.

gait analysis, sports

in typical or normal gait, knee flexion in swing is facilitated by:

hip flexor muscles and ankle plantar flexor (A and C)

surgical intervention called muscle lengthening involves which of the following:

incision of fascia followed by stretching of muscle

when a 2-D static equilibrium problem to find joint and muscle forces, like the examples discussed in class, ends up with more unknowns than the number of equations (sum of forces and moments), what can you do?

increase the number of equations by estimating force distributions in muscles & decrease the number go unknowns by grouping or ignoring muscles

strain gauges allow strain measurements based on voltage outputs because as the material of interest experiences deformation and the wires inside the strain gauge are stretched, the electrical resistance (increases/decreases).

increases

how is hamstring spasticity in late swing phase of gait thought to affect knee flexion/extension at the point of second initial contact?

increases knee flexion angle at second initial contact

figure 2 above shows the state of 2-D stress at a point p, computed in reference to two different coordinate systems (x-y, and x'-y'). as angle alpha between the two coordinate systems increases, the value of sigma xx' + sigma yy'

is always the same as sigma xx + sigma yy as long as acting on the same point

in performing push ups, holding the plank pose requires ___ contraction of muscles.

isometric

in studying gait, what kind of analysis requires force plate data?

kinetics

most soft biological tissues exhibit ___ and should be analyzed using ___

large deformation, exact measures of strain

the integrity of the hip is enhanced by the strong ___ crossing the joint.

ligaments

if the same material above was subjected to stretching at a slower rate, the stress-strain plot would shift to the right and the material would appear:

more compliant (more elastic is not a thing)

the stress-strain plot above exhibits which of the following behavior?

neither a nor b (not linear or elastic)

if a force acting on an area is parallel to the outward normal vector (of the area), then the force is called

normal force

as discussed in class, extra challenges in subject calibration arise because of which of the following?

obesity

specialized bone cells that are entrapped in one tissue are called what?

osteocytes

in an image showing the posterior view of the left forearm in supination (plan is hidden from the view), radius and ulna are:

parallel with each other and radius on left

suppose that a simply supported beam is subjected to a single point load acting transversely at the halfway point between two support as shown above. according to the positive sign convention used in your text, the bending moments are:

positive but not constant throughout

suppose that a simply supported beam is subjected to a single point load acting transversely at the halfway point between two supports as shown above. according to the positive sign convention used in your test, the shear forces are:

positive on the left-hand side and negative on the right-hand side

disruption of typical or normal ankle motion during gait can result in:

possibly all of the above: - disruption in knee motion as well - gait problems in stance phase - gait problems in swing phase

when a soft tissue specimen is cyclically loaded and unloaded for 3-10 cycles the material tends to exhibit repeatable pseudo elastic response. this experimental process is called ___.

preconditioning

mechanical stability of bone fracture fixation may be affected by:

quality of the bone

a "ghost marker":

refers to a motion data processing artifact

what is muscle spasticity?

reflexive muscle contraction in response to a quick stretch

give one example of bone fracture fixation technique/approach

screws

the motion described by the following displacement vector and as seen in the figure is referred to as

simple shear

the type of wrist injury that involves a fracture of the radius bone is called what?

smith's fracture

A subject calibration trial provides the relationship between reflective markers placed on the surface of the skin and the underlying anatomy. data are collected for this calibration trial while the subject is?

standing still

in mechanics problems such as the question above, when there are not a sufficient number of equations for the number of unknowns, such cases are called

statically indeterminate

Fung's idea to demonstrate the exponential form constitutive relations of soft tissues was to plot

stiffness vs. stress

the figure (a) above shows a metal hip prosthesis that replaced a damaged femoral head. when this hip subjected to leading with force, f:

stress is greater in prosthesis than in bone, but strain is the same in both

the term ___ refers to a condition when the implanted device is too rigid and carries too much of the stress, which can result in the weakening of the bone.

stress sheilding

the modern concept of stress defined in the 19th century states that stress is a measure of force acting over an oriented area. thus, mathematically, stress is a:

tensor

as a cantilevered beam with a rectangular cross-sectional area decreases in length (L), what has to happen to the thickness of the cantilever (h), if the base (b) remains the same, in order for the effective stiffness (k) to remain constant?

the thickness needs to decrease

the correct reason behind your choice for Question 1 is that:

there is not relative motion between the bone and prosthesis and the Young's modulus is greater for the prosthesis

the amount of ___ a muscle group can generate at a ___ is used to measure muscular strength.

torque, joint

name one other component of bone matrix besides hydroxyapatite (calcium + phosphate) minerals or cells.

type I collagen

mechanical behaviors of collagenous soft tissues (e.g. tendon) are governed mainly by change in entropy because

untangling of chain-like molecules

BMI (body mass index) is calculated by

weight divided by the square of height

give one example of an experimental (or physical) condition (not material composition) that influences the constitutive behavior of a material.

wetting/hydration of material

when normal stress is at the maximum (sigma xx' = sigma 1 at alpha = alpha p), the shear stress (sigma xy') at the same point (under the same coordinate system) is

zero

which one of the following numbers may be considered hypertension?

140/90 mmHg

motion capture cameras acquire images of reflective markers placed on the test subject. what is the minimum number of markers required for each body segment for the observer to measure the 3D movement of that segment?

3

in 2-D, the exact measure of Green strain has

3 independent components

multiple synchronized motion camera images of reflective markers are used to mathematically determine the:

3-D locations of the markers relative to the laboratory coordinate system

the earlier concept of stress was defined in the 18th century by:

Euler

the authors of the required textbook for BIOE 3200 are:

Humphrey and O'Rourke

in the stance phase of the gait cycle, what muscle group produces an ankle moment to control the forward movement of the tibia over the plantigrade foot (when the plantar surface of the foot is entirely on the ground)?

ankle plantar flexor muscles (calf muscles)

the world congress of biomechanics 2014 took place in:

USA

according to Fung's observation most soft tissues exhibit

a and c: hysteresis & strain-rate insensitivity

typical treatments for occlusive coronary artery disease include:

a, b, and c: balloon angioplasty, bypass surgery & endovascular stents

__ muscles stabilize the pelvis during the support phase of walking and running and when you stand on one leg.

abductor

in cell-matrix adhesion, vinculin proteins in focal adhesions link the extracellular matrix to ___ within the cell.

actin filaments

only two motion capture cameras are required to determine the location of a reflective marker. And yet, most clinical motion labs have 8 to 12 motion capture cameras. why? the additional cameras:

all of the above: - allow markers on the from and back and each side of the body to all be seen - allow markers that are visually hidden by crutches, walkers or other walking aides in some camera views to be adequately monitored by other cameras - improve the precision of the measured marker location data

endothelial cells located at the site of a partially clogged artery experience which of the following distributed forces?

all of the above: - increased shear stress - increased pressure - increased circumferential strain

if you were tasked with investigating the effect of membrane tension on the activation of ion channels located in the cell membrane, which experimental approaches might you utilize?

all of the above: - micropipette aspiration - magnetic twisting cytometry - optical tweezers

what can cause a foot to "point" inward during gait?

all of the above: - the shape of the foot - an abnormal twist of the tibia - an abnormal twist of the femur

why is the concept of processive motors important in the explanation of dynein and kinesin motor proteins?

all of the above: - increases motor run lengths - generates larger forces - allows for vesicle transport

a condition characterized by enlargement of the diameter due to weakening of the aortic wall tissue is known as ___.

aneurysm

when subjected to planar, equi-biaxial, tensile forces (same magnitude in two orthogonal directions) a heart valve leaflet tissue with dominant collagen fiber orientation in one direction will exhibit greater extension in cross-fiber direction. this is a manifestation of:

anisotropic behavior

in Hooke's law, the parameter that relates strain (epsilon) to change in temperature (delta T) is called what?

coefficient of thermal expansion

overweight and obese individuals are at increases risk for which of the following?

coronary heart disease, type 2 diabetes, hypertension

muscles' tension generating capacity is dependent on:

cross sectional area of muscle fibers & training state of the muscle

in an image showing the anterior view of the right forearm in pronation (palm is hidden from view), radius and ulna are:

crossed with each other and radius on top

a motion described by the following displacement vector and as seen in the figure is referred to as rigid body rotation, which Green strains are insensitive too. what part of motion fo Green strains measure?

deformation (stretch + shear)

in a generic form of constitutive equation, stress can be determined as:

derivative of strain energy with respect to strain

for Question 2, the assumption used is called

displacement compatibility

according to Cauchy's definition, strains are a combination of ___

displacement gradients

how is rectus femurs spasticity in early swing phase of gait thought to affect knee motion in early swing phase?

disrupts the knee flexing motion that normally occurs in early swing

the space between loading and unloading curves in the plot above is known as hysteresis, which results from:

dissipation of energy

shear strain is a measure of

distortion angle

a cantilever beam is supporting a load as shown in the figure below.

downward sloping linear triangle

it has been observed that there exists so-called "residual stress" or "preloads" within vascular tissues that arises during development. as a result, when a segment of an artery is cut out of the body it tends to shrink. imagine a fresh-cut cross section of an artery ( like an onion ring), if one side is cut open (going from an "O"-shape to a "C"-shape) what will happen to the opening?

ends will pull away from each other