# thesIt

• #### Arif 12:19:08 pm on August 22, 2010 | 0 | # | Tags: basic, error, residual error, statistical error, wikipedia

If we assume a normally distributed population with mean μ and standard deviation σ, and take sample

$x_{1}, x_{2},..., x_{n}\sim N(\mu,\sigma^{2})$

statistical error is then
$\varepsilon_{i}=x_{i}-\mu$

## Residual

while residual is
$\hat{\varepsilon}_{i}=x_{i}-\bar{x}$

hat over the letter ε indicates an observable estimate of an unobservable quantity called ε.

• #### Arif 06:43:00 am on August 22, 2010 | 0 | # | Tags: basic, viscosity, wikipedia

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress.

The cgs physical unit for dynamic viscosity is the poise (P), more commonly expressed, particularly in ASTM standards, as centipoise (cP)

• #### Arif 06:32:12 am on August 22, 2010 | 0 | # | Tags: basic, density, wikipedia

Density of a material is defined as its mass per unit volume.
ρ (in some countries i.e. USA) is also defined as weight per unit volume
Units: (kg/m³), g/cm³

• #### Arif 10:56:17 am on February 27, 2010 | 0 | # | Tags: basic, pH, wikipedia

pH is a measure of the acidity or basicity of a solution, defined as minus the decimal logarithm of the hydrogen ion activity in a solution.

$pH=- log_{10} (a_{H^{+}})$

common pH scale (can't find where water is?)

• #### Arif 12:39:21 pm on February 21, 2010 | 0 | # | Tags: basic, viscosity, wikipedia

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensional stress. In everyday terms (and for fluids only), viscosity is “thickness”. Thus, water is “thin”, having a lower viscosity, while honey is “thick”, having a higher viscosity.

Viscosity describes a fluid’s internal resistance to flow and may be thought of as a measure of fluid friction. See Newton’ expression: the constant μ is known as the coefficient of viscosity, the viscosity, the dynamic viscosity, or the Newtonian viscosity.

• #### Arif 12:06:03 pm on February 19, 2010 | 0 | # | Tags: angular velocity, density, equation, interfacial tension, spinning drop, wikipedia

Interfacial tension and centrifugal forces balanced at mechanical equilibrium.

centrifugal-IFT equilibrium

Interfacial tension of any liquid that gives a shape very close to a cylinder at the equilibrium point, can be estimated using Vonnegut’s expression:

$\sigma=\frac{\Delta\rho\omega^2}{4}R^3$

ω : angular velocity; (radians per second, degrees per second, revolutions per second)

Δρ : difference between two fluid: the less-dense and the dense

• #### Arif 11:49:55 am on February 19, 2010 | 0 | # | Tags: basic, interfacial tension, spinning drop, tensiometer, wikipedia

Spinning drop method (rotating drop method) is one of the methods that is used to measure interfacial tension. Basically, measurements are carried out in a rotating horizontal tube which contains a dense fluid. One drop of a less dense liquid is placed inside the fluid.

Since the rotation of the horizontal tube creates a centrifugal force towards the tube walls, the liquid drop starts to be elongated and this elongation stops when the interfacial tension and centrifugal forces are balanced. Values obtained at this equilibrium point are used to estimate surface tension of the particular liquid by using appropriate correlations. A device called “spinning drop tensiometer” is generally utilized for this purpose.

• #### Arif 12:22:45 pm on February 17, 2010 | 0 | # | Tags: basic, interfacial tension, wikipedia, Young-Laplace

osculating circle

radius of curvature of a curve at a point is the radius of the osculating circle at that point.

• #### Arif 04:55:12 pm on January 6, 2010 | 0 | # | Tags: basic, spectrophotometry, wikipedia

how spectrophotometer works

There are two major classes of devices: (1) single beam and (2) double beam. A double beam spectrophotometer compares the light intensity between two light paths, one path containing a reference sample and the other the test sample.

Wikipedia File:Spetrophotometer-en.svg

In short, the sequence of events in a spectrophotometer is as follows:

1. The light source shines into a monochromator.
2. A particular output wavelength is selected and beamed at the sample.
3. The sample absorbs light.

intensity of that particular wavelength (I vs nm) is recorded.

• #### Arif 04:50:35 pm on January 6, 2010 | 0 | # | Tags: basic, spectrophotometry, wikipedia

A spectrophotometer is a photometer (a device for measuring light intensity) that can measure intensity as a function of the color (or more specifically the wavelength) of light.

• Next Page »