BET equation SlideShare

Bet isotherm - SlideShar

The summation represented in the numerator and denominator is merely the sum of an infinite geometrical progressions (G.P) we also have that, So , equation 9 reduce to Equation (10) is known as B.E.T. equation 24. Comment on the BET isotherm BET equation fits reasonably well all known adsorption isotherms observed so far (types I to V) for. So Langmuir equation reduces to. θ = KP • At high pressure KP is so large, that factor (1+KP) in denominator is nearly equal to KP. So Langmuir equation reduces to. 13. BET adsorption Isotherm • BET Theory put forward by Brunauer, Emmett and Teller explained that multilayer formation is the true picture of physical Adsorption Equation (1) is an adsorption isotherm and can be plotted as a straight line with / [(/)] on the y-axis and = / on the x-axis according to experimental results. This plot is called a BET plot.The linear relationship of this equation is maintained only in the range of < / <.The value of the slope and the y-intercept of the line are used to calculate the monolayer adsorbed gas quantity and the.

SOP: Specific surface area analysis by BET theory Page 1 of 5 Specific surface area analysis by BET theory Specific surface area by Brunauer-Emmett-Teller (BET) theory Date 30.05.2016 Version 1.0 English Contents 1 Scope 2 2 Basics 2 2.1 Background: BET theory 2 3 Materials & Instruments 2 3.1 Materials 2 3.2 Instruments by Clausius-Clapeyron equation 2) ln (RT H T p ads v Δ =− ∂ ∂ for physical adsorption, Hads ≈ heat of condensation z For example : heat of condensation of N2 = -6 KJ/mole Hads of N2 on iron = -10 KJ/ mole on graphite = -12KJ/mole on TiO2 = -14 KJ/mole chemisorption of N2 on iron = -150 KJ/mol If BET equation, when P/P 0 <<1 and c>>1, then it leads to monolayer formation and Type I Adsorption Isotherm is obtained. The reversible Type I isotherm is concave to the relative pressure, p/p° axis and a approaches a limiting value as p/p° ~ 1

In BET equation, value of C has to be very large in comparison to 1. Examples of Type-II adsorption are Nitrogen (N 2 (g)) adsorbed at -1950°C on Iron (Fe) catalyst and Nitrogen (N 2 (g)) adsorbed at -1950°C on silica gel. Type III Adsorption Isotherm: Type III Adsorption Isotherm The BET equation (named after Brunauer, Emmett, and Teller who developed the theory) was first published in 1938 (Brunauer, 1938), and continues to be the most widely used method to determine the number of molecules/atoms of a gas needed to form a monolayer, X m, of adsorbed gas on a solid surface (Thommes, 2015).The BET equation (Equation 1) describes the relationship between the number of. Thermodynamic Derivation. The adsorption process between gas phase molecules, A, vacant surface sites, S, and occupied surface sites, SA, can be represented by the equation, assuming that there are a fixed number of surface sites present on the surface. An equilibrium constant, K, can be written: q = Fraction of surface sites occupied (0 < q < 1 The equation for BET is. Applications of Adsorption. Following are the applications of adsorption: Gas masks: Poisonous gases get adsorbed to at the surface of the mask and prevent its encounter when used by coal miners. Production of vacuum: Traces of air are adsorbed on charcoal and removed from devices undergoing the process of evacuation

BET surface area analysis - SlideShar

BET (brunour emet teller )Isotherm: By fitting experimental data to the empirical equation, the monolayer (potential) water content can be derived.It is a very interesting parameter, because when the moisture content equals to the monolayer water, the food reaches the highest stability.It is an interesting parameter to know, because when drying food it is not recommended to dry further than. The BET isotherm has the form: Both the Laugmuir equation and the BET equation were developed basing on similar assumptions. However, t'he Langmuir equation assumed a monolayer adsorp- tion and the BET equation extended Langmuir's idea to multiple layer adsorption

The BET monolayer . The Zone 1-Zone 2 boundary is hard to measure directly on a real isotherm as the curves tend to be very broad and the point of inflection is poorly defined. Some better understanding of the monolayer value can be found by fitting a theoretical equation to the measured data and using the theory to calculate the monolayer value Derivation of Beat Frequency Formula: Consider sound from two different sources whose medium is air is meeting at a point p. Let us assume that one source has a shorter time period as T S and high frequency as f 2 whereas other source time periods and frequency are T L and f 1.With the help of these frequencies, we represent beat frequency by showing the relationship between these two frequencies

The BET (Brunauer -Emmett -Teller) surface area measurement was made using a conventional BET multi-point N 2 physisorption apparatus (Gemini 2360, Micromeritics Instruments Corp). The N 2 adsorption was measured from a six-point isotherm in a relative pressure rang of 0.05 to 0.3 at 77.3 K. The assumption for the cross-sectional area of S(BET Vm(DR) 0.000001 1000 800 600 200 Sample Maxsorb Carbosieve Norit 0.6 Relative pressure 0.8 Maxsorb Carbosieve Norit 0.2 rn2/g 2100 1120 970 cm3/g 0.69 0.42 0.37 J. Jagiello, A. Anson, M.T. Martinez, J. Phys. Chem., 110 (2006) 4531 micromeritic AS-3012 is a BET Analyzer that performs surface area analysis on ISO 9277. ISO 9277 is about determination of the specific surface area of solids by gas adsorption using the BET method.AS-3012 works on the principle of the popular physical adsorption isotherms, specifically static volumetric method.The computer controls the operation automatically without any human monitoring viscosity. The Wen and Yu equation (4) is a second-order polynomial with respect to the particle Reynolds number calculated at the minimum fluidization velocity, Rep,mf: After calculating the Archimedes number, the Reynolds number can be determined using the quadratic equation or an equation solver. Finally, the minimum fluidization velocity, m In order to construct a utility index based on the N-M equation, we have to assign utility values С and B. These utility values are arbitrary except for the fact that higher value should be assigned to a preferred event (lottery). Suppose we assign the following arbitrary utility values: U c = 100 utils, U b =0 util, and P= 4/5 or 0.8, the

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Derivation of Bet equation and different isotherm

Adsorption isotherm - SlideShar

Power Point Presentation (.PPT) in Genetics Free Download from Slideshare for Students and Teachers. Simplified PPTs for Easy Genetics Teaching and Learning ESS210B Prof. Jin-Yi Yu R2--value R2-value measures the percentage of variation in the values of the dependent variable that can be explained by the variation in the independent variable. R2-value varies from 0 to 1. A value of 0.7654 means that 76.54% of th Several methods can be employed to directly measure rock porosity: (1) saturation or imbibition, (2) buoyancy, (3) gas expansion (He porosimetry), (4) gas adsorption (BET) and (5) mercury intrusion porosimetry (e.g., Tiab and Donaldson 2004; Sondergeld et al. 2010; Clarkson et al. 2012c). All five of these methods only measure the effective. 15. List the conditions to be met to use the Langmuir isotherm. 16. List 5 techniques that are suitable to the study solid surfaces. 17. Mention 3 methods which are suitable to determine the diffusion coefficient. 18. Give practical application examples for thixotropic materials. 19. Give examples for shear thinning materials. 20. Give examples for shear thickening materials

Adsorption isotherms - SlideShar

  1. The top equation says 'if A is divided into 3 pieces then P (A) is the sum of the probabilities of the pieces'. The bottom equation (3) is called the law of total probability. It is just a rewriting of the top equation using the multiplication rule. 18.05
  2. The BET equation (equation 4), which is the most widely used model in food systems, was first proposed by Brunauer, Emmett and Teller (23). It represents a fundamental milestone in the interpretation of multi-layer sorption isotherms, particularly the types II and III. It is also an effective method for estimating the amount of bound water in.
  3. g a Fourier Transform (FT) on the interferogram to obtain the spectrum. An FT-IR spectrometer collects and digitizes.
  4. should take my bet because the probability that the ball has a number between −1.00 and +1.00 is 68.26%. Therefore, you would roughly have a 68% chance of winning, and I would only have a 32% chance of winning. How about if we up the stakes? I will bet you $100 that a z score on a randomly chosen ball is greater than +2.00 or less than −2.
  5. The Capital Asset Pricing Model (CAPM) describes the relationship between systematic risk and expected return for assets, particularly stocks. CAPM is widely used throughout finance for pricing.

Porosity or void fraction is a measure of the void (i.e. empty) spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure the accessible void, the total amount of void space accessible from the surface (cf. closed-cell foam).. There are many ways to test porosity in a. Beta-Carotene is a naturally-occurring retinol (vitamin A) precursor obtained from certain fruits and vegetables with potential antineoplastic and chemopreventive activities. As an anti-oxidant, beta carotene inhibits free-radical damage to DNA. This agent also induces cell differentiation and apoptosis of some tumor cell types, particularly in early stages of tumorigenesis, and enhances. Y. Artioli, in Encyclopedia of Ecology, 2008 Equations for Adsorption. As discussed in the previous section, adsorption usually involves low enthalpy and has a short lifetime. This means that adsorption and desorption have low activation energy, and then the amount of molecules adsorbed/desorbed from the adsorbent is very high: equilibrium is reached fast, if physicochemical environmental. Objectives Describe the normal cardiac anatomy and physiology and normal electrical conduction through the heart. Identify and relate waveforms to the cardiac cycle

Derivation of Bet equation and different isotherms

by the equation R = 8ηℓ/πr4 (where η = viscosity, ℓ = length of tube, and r = internal radius of the tube), which is derived from Poiseuille's Law.1,8,9 When the tube is lengthened or narrowed, resistance increases. Over time, new ven-tilator techniques have evolved to reduce the work of breathing associate Calculating the breakeven point is a key financial analysis tool used by business owners. Once you know the fixed and variable costs for the product your business produces or a good approximation of them, you can use that information to calculate your company's breakeven point. Small business owners can use the calculation to determine how many product units they need to sell at a given price. An ordinary differential equation in explicit form is an equation y′(t) = f(t,y) where y′(t) is meant to be the derivative of ywith respect to time tand fis a function of time tand current state y. A solution is a differentiable function Y which satisfies this equation when substituted into the differential equation, i.e., when.

BET theory - Wikipedi

Now, the second equation can be rewritten as : This is known as Conditional Probability. Let's try to answer a betting problem with this technique. Suppose, B be the event of winning of James Hunt. A be the event of raining. Therefore, P(A) =1/2, since it rained twice out of four days. P(B) is 1/4, since James won only one race out of four 10. Sketch your circle, and write an equation relating m∠. BAC. and the measure of arc . BC. 11. Name your file as directed by your teacher. Inscribed Angles . 1. Open a new sketch. 2. Draw a circle. Label the center . A. and a point on the circle . B. 3. Draw a second point on the circle, and label it . C. 4. Draw a third point on the circle. (1958), equation (4) does not allow for the effect of the adsorption forces on the meniscus curva-ture and is also likely to vary with the distance from the surface. Returning to the question of the origin of physisorption hysteresis, we now see that there are several ways in which capillary condensation may play a central role Parametric equations of lines General parametric equations In this part of the unit we are going to look at parametric curves. This is simply the idea that a point moving in space traces out a path over time. Thus there are four variables to consider, the position of the point (x,y,z) and an independent variable t, which we can think of as time

The USP Endotoxin RS has a defined potency of 10,000 USP Endotoxin Units (EU) per vial. Constitute the entire contents of 1 vial of the RSE with 5 mL of LAL Reagent Water 3, mix intermittently for 30 minutes, using a vortex mixer, and use this concentrate for making appropriate serial dilutions.Preserve the concentrate in a refrigerator for making subsequent dilutions for not more than 14 days Solve the appropriate equation for the quantity to be determined (the unknown). Note that the change in entropy can be determined between any states by calculating it for a reversible process. Substitute the known value along with their units into the appropriate equation, and obtain numerical solutions complete with units Basic Trig Identities. The basic trig identities or fundamental trigonometric identities are actually those trigonometric functions which are true each time for variables.So, these trig identities portray certain functions of at least one angle (it could be more angles). It is identified with a unit circle where the connection between the lines and angles in a Cartesian plane 1.4.2 Electric Double Layer. An electric double layer is a phenomenon that plays a fundamental role in the mechanism of the electrostatic stabilization of colloids. Colloidal particles gain negative electric charge when negatively charged ions of the dispersion medium are adsorbed on the particle surface Equation (13) is applicable only to the early stages of decomposition, (BET) method. Typical for CPG, the distribution was rather narrow so for an average pore radius of 3.5 nm the distribution had a full width at half maximum height equal to about 0.5 nm, or 14%. CPG with similar narrow distributions can be produced with a large variety of.

The word Transistor is a combination of the two words Trans fer Var istor which describes their mode of operation way back in their early days of electronics development. There are two basic types of bipolar transistor construction, PNP and NPN, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made The second part of the equation (in black) describes the exchange between CO 2 and H 2 O depending on the partial pressure of the sorbate. Hence, e.g. only a site already covered with CO 2 can be replaced by H 2 O and vice versa. The last part of the equation (in blue) accounts for desorption of both CO 2 and H 2 O from site C upon thermal. Adsorption isotherm is a curve that expresses the variation in the amount of gas adsorbed by the adsorbent with the temperature at constant pressure. Freundlich isotherm fails at high pressure. If the plot of log x/m on the y-axis and log P on the x-axis is a straight line, then Freundlich isotherm is valid

Adsorption Isotherm (Theory) : Physical Chemistry Virtual

Differential scanning calorimetry (DSC) is a thermoanalytical technique used to study the thermal properties of the polymer using a differential scanning calorimeter. In this process, the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature Rise (r) : must be between 150 and 220mm. Going (g): must be between 220 and 300mm. Pitch angle : anything up to a maximum of 42 degrees. But there is a further criterion, one which constrains the relationship between the going and riser, namely: g+2r = 550mm to 700mm. I've always been aware of this equation X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline material and can provide information on unit cell dimensions. The analyzed material is finely ground, homogenized, and average bulk composition is determined

201093955 adsorbtion

BET Theory :: Anton Paar Wik

Equation (27) is a simple equation that can be used to verify the theory for the Compton Effect. The energy of incident gamma rays E can be easily measured with a scintillator-photomutiplier detector and multichannel analyzer system. The energy of the scattered gamma rays E' as a function of can also be easily measured with the same system. Asset turnover is the ratio of a company's sales compared to the value of its average operating assets. This ratio can be an indicator of the efficiency with which a company is using its assets in generating revenue. The formula is Sales or Revenues / Total Assets = Asset Turnover. For example, $100,000 sales / $80,000 assets = 1.25 By the end of this course, you'll be able to solve any equation with ease. And I bet, you might even think it's actually fun. So jump aboard, and let's get started solving equations

Connect with friends and the world around you on Facebook. Create a Page for a celebrity, band or business You bet! Chegg Study Expert Q&A is a great place to find help on problem sets and Quantum Physics study guides. Just post a question you need help with, and one of our experts will provide a custom solution. You can also find solutions immediately by searching the millions of fully answered study questions in our archive

Adsorption isotherm

Derivation of the Langmuir and BET Isotherm

(a) Consider a situation in which the forpe F applied to a particle of mass m is zero. Multiply the scalar form of Eq. (1.2) on page 7 (i.e., a = dv/dt) by dt, and integrate both sides to show that the velocity v (also a scalar) is constant. Then use the scalar form of Eq. (l.l) to show that the (scalar) position r is a linear function of time Some of you may remember J.R. Ewing on the television show called Dallas that ran from 1978 through 1991. J.R. Ewing, a greedy and unethical oil tycoon was one of the main characters. The series was utterly mesmerizing, and literally everyone tuned in Equation 1 is easily derived, as detailed in Ref. 2 and other sources. Adsorption can be used to treat waste streams or purify valuable components of a feed. This article describes both equilibrium and mass-transfer considerations, and reviews the fundamentals of adsorption system design. Alan Gabelman, P.E. Gabelman Process Solutions, LL

Adsorption Isotherms - Freundlich Adsorption Isotherms

From the PFR module we have. The catalyst weight and rector volume are related by the catalyst bulk density (g/dm 3). The reaction rate per unit volume and the reaction rate per unit catalyst weight are also related by the bulk density, r b The differential form of the PBR mole balance i Beta Distribution Definition. The beta distribution is a family of continuous probability distributions set on the interval [0, 1] having two positive shape parameters, expressed by α and β. These two parameters appear as exponents of the random variable and manage the shape of the distribution. Usually, the basic distribution is known as the. This is Bragg's lawin its simplest form. ff X-Ray Diffraction • Bragg equation relates the spacing between adjacent crystal planes and the angle of diffraction. = 2d sin d spacing between crystal planes angle of scattering wavelength of x-ray beam 2 diffraction angle. fDiffraction of X-ray by Lattice Planes f X-ray Diffraction in. Implication from the Laplace equation For porous solids, we can imagine a pore to be cylindrical capillary of radius r, when r ↓ p↑ vapor will condense in small capillaries at pressures less than the normal pressure P0(defined for planar surface) for Type IV and V isotherms, condensation occurs at P<P Equation 6.2 can then be written Ii = zie ciui E = σi E (6.4) where σi = zie ciui is the electrical conductivity due to the charge carriers of type i. The electrical conductivity is determined by the product of the concentration ci of the charged particles, the charge zie on the particles and the charge carrier mobility, ui. It should be note

Power Point Presentation (.PPT) in Biochemistry Free Download from Slideshare for Students. Simplified PPTs for Easy Biochemistry Teaching and Learning As can be seen from the equation, the total heat flow (dQ dt), which is the only heat flow measured by conven-tional DSC, is composed of two components. One component is a function of the sample's heat capacity and rate of temperature change, and the other is a function of absolute temperature and time 284 2179-2182. [This indicates an equation to estimate the nitrogen fixed by lupinus using the 15N natural abundance]. Bardin R., Domenach A.M. and Chalamet A. (1977). Rapports isotopiques naturels de l'azote II. Application à la mesure de la fixation symbiotique de l'azote in situ. Revue d'Ecologie et de Biologie du Sol 14, 395-402 Cartesian Plane (X Y Graph) Definition. A Cartesian plane is a graph with one x-axis and one y-axis (that's why it's sometimes called an X Y graph). These two axes are perpendicular to each other. The origin (O) is in the exact center of the graph. Numbers to the right of the zero on the x-axis are positive; numbers to the left of zero are.

foodtech: Water Sorption Isother

  1. Fission products Strontium. Strontium-90 is a commonly used beta emitter used in industrial sources. It decays to yttrium-90, which is itself a beta emitter.It is also used as a thermal power source in radioisotope thermoelectric generator (RTG) power packs. These use heat produced by radioactive decay of strontium-90 to generate heat, which can be converted to electricity using a thermocouple
  2. Assume there is no salvage value at the end of the project and the required rate of return is 8%. The NPV of the project is calculated as follows: N P V = $ 5 0 0 ( 1 + 0. 0 8) 1 + $ 3 0 0 ( 1 + 0.
  3. fundamentals of differential equations 8th edition pdf Calculation plays an important role in modern mathematics education. The calculation is called economic studies, science and engineering. Integral calculus is an important part of the fundamental theorem of calculation and plays an important part of our daily life. This is also called particle physics
  4. The certainty equivalent is a guaranteed return that someone would accept, rather than taking a chance on a higher, but uncertain, return
  5. g nitrobenzene. Sulfonation of Benzen
  6. For a given Mach number, M 1, and corner angle, θ, the oblique shock angle, β, and the downstream Mach number, M 2, can be calculated.Unlike after a normal shock where M 2 must always be less than 1, in oblique shock M 2 can be supersonic (weak shock wave) or subsonic (strong shock wave). Weak solutions are often observed in flow geometries open to atmosphere (such as on the outside of a.

Food Chemistry - Pennsylvania State Universit

  1. Wage equation The last ingredient of the Classical Theory of Unemployment is the wage schedule or wage equation. This equation explains how the salaries are set up by external agents (like labor unions) and employees through collective or individual bargaining over the competitive level
  2. Adsorption is a process accumulation of a substance in molecular species in higher concentration on the surface. Get detailed notes on the adsorption types, isotherms, calculation and more at BYJU'S
  3. anything within a factor of 2, I am more confident, even willing to place a bet at 2 to 1 odds, that I am in the right. But go check it out: Jane's All the World's Air­ craft will serve as a resource. Is the method correct? The criteria here are more certain: In the first place, it is essential that I identify the lift force as the weight
  4. ation of.
  5. The IPAT Equation: I = P x A x T. A classic attempt to explain the relationship between a human population and its impact on the environment is the IPAT equation. The equation maintains that impacts on ecosystems (I) are the product of the population size (P), affluence (A), and technology (T) of the human population in question
  6. Purpose: Pes planus, or flat feet, is estimated to affect approximately 3-25% of the adult population globally. An explanation for this variability in prevalence is the use of a wide variety of methods ranging from self report to footprint based measurements to diagnose foot type. Clinicians often observe that patients with pes planus are afflicted with pathologies in the medial forefoot, arch.

The Monte Carlo analysis is a decision-making tool that can help an investor or manager determine the degree of risk that an action entails vii Contents PREFACE xvii ABOUT THE AUTHOR xxxiii CHAPTER 1 MOLE BALANCES 1 1.1 The Rate of Reaction, -r A 4 1.2 The General Mole Balance Equation 8 1.3 Batch Reactors (BRs) 10 1.4 Continuous-Flow Reactors 12 1.4.1 Continuous-Stirred Tank Reactor (CSTR) 12 1.4.2 Tubular Reactor 14 1.4.3 Packed-Bed Reactor (PBR) 18 1.5 Industrial Reactors 22 CHAPTER 2 CONVERSION AND REACTOR SIZING 3

Solving an equation is the process of getting what you're looking for, or solving for, on one side of the equals sign and everything else on the other side.You're really sorting information. If you're solving for x, you must getx on one side by itself.. Addition and subtraction equations Metal-organic frameworks (MOFs) are a relatively new class of porous, crystalline materials with a broad range of applications. MOFs are composed of metal ions or clusters, which act as the joints, bound by multidirectional organic ligands, which act as linkers in the network structure. These networks can be 1-D, 2-D, or 3-D extended, periodic. Free Educational Notes, Video Lectures and Study Material. Download PDF Note 4 Chapter 13 - Formulation of Parenteral Products Introduction to Parenteral Products Basic theory Parenteral (para enteron—beside the intestine) administration is the introduction into the body of nutrition, medications, or other substances other than by the alimentary canal

Beat Frequency Formula: Definition, Formula Derivation

  1. The above equations are W-H equations. A plot is drawn with 4sin along the x-axis and hkl cos along the y-axis for as-prepared ZnO nanoparticles as shown in Figure 2.From the linear fit to the data, the crystalline size was estimated from the y-intercept, and the strain , from the slope of the fit.Equation5 represents the UDM, where the strain was assumed to be uniform in all crystallographic.
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  3. 4.1.2 Median. The median is the middle-value that occurs when the data are arranged in an ascending or descending order, and is commonly denoted by the symbol \(Md\).Since central tendency is all about finding the center of the values of a variable \(x\), the median tends to be intuitive for most folks and calculating it is equally simple..
  4. Here are 20 potential uses for blockchain technology. 1. Payment processing and money transfers. Arguably the most logical use for blockchain is as a means to expedite the transfer of funds from.
  5. e each of the other lixels that are reachable from their position given the current h l using.
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  7. The equations of motion of a system can be derived by a number of different methods. These are derived here by using Lagrange's Equa­ tions(l4), the energy method most frequently encountered in engineering analysis. To use Lagrange's equation, it is necessary to define: (1) Generalized Coordinates: A set of independent coordinates use

You bet! Chegg Study Expert Q&A is a great place to find help on problem sets and Math study guides. Just post a question you need help with, and one of our experts will provide a custom solution. You can also find solutions immediately by searching the millions of fully answered study questions in our archive The work of expansion can be depicted graphically as the area under the p-V curve depicting the expansion. Comparing examples \(\PageIndex{1}\) and \(3.1.2\), for which the initial and final volumes were the same, and the constant external pressure of the irreversible expansion was the same as the final pressure of the reversible expansion, such a graph looks as follows Relative risk is a statistical term used to describe the chances of a certain event occurring among one group versus another. It is commonly used in epidemiology and evidence-based medicine, where relative risk helps identify the probability of developing a disease after an exposure (e.g., a drug treatment or an environmental event) versus the chance of developing the disease in the absence of. Monte Carlo simulations are used to model the probability of different outcomes in a process that cannot easily be predicted due to the intervention of random variables. It is a technique used to. Weather & Climate. Surface tension is a phenomenon in which the surface of a liquid, where the liquid is in contact with a gas, acts as a thin elastic sheet. This term is typically used only when the liquid surface is in contact with gas (such as the air). If the surface is between two liquids (such as water and oil), it is called interface.