GGRB28H3 Chapter : Week 9 Article 1.docx

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blackplatypus827

8 Apr 2012

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The association of housing density, isolation, and tuberculosis in canadian first nations communities. Early 20th century; death rate from t. b. in first nations in canada was 700/100 000. Due to malnutrition, confinement on crowded reservations with poor sanitation, & lack of immunity to the tb bacillus. In 1999, rate was 10 times that of the overall canadian rate in 1997. Association has been recognized between overcrowded housing and t. b. incidence, paediatric tb, & tb mortality. T. b. incidence higher in communities which are isolated from health services. All forms of t. b. were included; pulmonary & extrapulmonary. Housing density expressed as the average number or persons per room (ppr) in a community, and household income is expressed in canadian dollars. Average housing density higher in first nations (f. n. ) (0. 7 ppr), than in non-aboriginal canadian population (0. 4 ppr) Tb rates highest in saskatchewan, then alberta and manitoba. The 3 provinces have highest average levels of housing density.

Related Questions

A plane electromagnetic wave varies sinusoidally at 90.0 MHz as its travels through vacuum along the positive x direction. The peak value of the electric field is 2.00 mV/m, and it is directed along the positive y direction. Find (a) the wavelength, (b) the period, and (c) the maximum value of the magnetic field. (d) write the expression in SI units for the space and time variations of the electric field and of the magnetic field. Include both numerical values and unit vectors to indicate direction. (e) find the average power per unit area this wave carries through space. (f) find the average energy density in the radiation (in joules per cubic meter) (g) what radiation pressure would this wave exert upon a perfectly reflecting surface at normal incidence?

erinrhinoceros274

Desperately need help on this problem i have triedeverything!

A solar sail allows a spacecraft to use radiation pressure forpropulsion, similar to the way wind propels a sailboat. The sailsof such spacecraft are made out of enormous reflecting panels. Thearea of the panels is maximized to catch the largest number ofincident photons, thus maximizing the momentum transfer from theincident radiation.

For such spacecraft to work, the force from the radiation pressureexerted by the photons must be greater than the gravitationalattraction to the star emitting the photons. The critical parameteris the area density (mass per unit area) of the sail.

Consider a perfectly reflecting mirror oriented so that solarradiation of intensity I is incident upon, and perpendicular to,the reflective surface of the mirror. If the mirror has surfacearea A, what is F_rad, the magnitude of the average force due tothe radiation pressure of the sunlight on the mirror?
Express your answer in terms of the intensity I, the mirror'ssurface area A, and the speed of light c.

my answersreview part

To solve the second part of this problem you will need to know thefollowing:

* the mass of the sun, M_{\rm sun} = 2.0\times10^{30}\;{\rmkg},
* the intensity of sunlight as a function of the distance R fromthe sun,

I (sun)(R) = 3.2\times10^{25}\,\frac{1}{R^2}\;({\rm W/m^2}),
and
* the gravitational constant G = 6.67 \times 10^{-11}\; {\rmm^3}/({\rm kg}\cdot {\rm s^2})\;.

Part B
Suppose that the mirror described in Part A is initially at rest adistance R away from the sun. What is the critical value of areadensity for the mirror at which the radiation pressure exactlycancels out the gravitational attraction from the sun?

I found part A, but cannot find part B

GGRB28H3 Chapter : Week 9 Article 1.docx

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