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  • Khalid Hassan added an answer in T-Test:
    Minimum sample size for t-test??

    Hi all.. I have been quite confused with statistical tests.. I think my doubt is very preliminary but I am not sure.. I have two populations (treated and un-treated) each with n=3. I would like to know if t-test can be used for a small population? I have read in some websites that t-test was introduced for small sample size but some say you would need at least 20. I understand that for low sample size, the population would assumed to be normally distributed but would it be correct to convert them into log and then perform the t-test??

    Or would Mann Whitney be a better test for low sample size??? The problem I feel with U test is that it is based on ranks and doesn't consider standard deviation (based on what I understood). Also, I compare treated and non-treated samples and that treated samples will have higher values in most cases and so U and U critical would be 0 (since n1=3 and n2=3 and p=0.05*2 as I use one-tailed, Ucric = 0).

    I hope I have explained my question clearly. Please provide your suggestions. Thank you!!

    Khalid Hassan · University of Diyala

    I confime the notes of Ariel Linden mentioned prviously ,  

    You can use Gpower software ( avaliable as free version in the web ) to calculate sample size for many types of tests . 

    also, you can get information about sample size calculation from the attacments files

    Good Luck

  • Kåre Olaussen added an answer in Special Relativity:
    Is the neutrino rest-mass a reality, or is an illusion?

    I am no specialist in the topic of neutrino flavor oscillations, but I examined a lot of articles, theoretical and experimental, on this topic. And the result is that I remained with doubts on whether the neutrinos really have a rest-mass.

    Here are some of my doubts.

    1. The velocity of the neutrino is extremely close to that of the light. The theory of the flavor oscillation requires, in order to be able to see such oscillations, to have  r = ct, where r is the distance travelled by the neutrino and t the travel time.

    2. The extremely low values found for the presumed rest-masses ~ 10-3eV (i.e. 1.7x10-35gr.)

    2. In a correct quantum treatment of the neutrino, i.e. as a wave-packet of limited dimensions, the neutrino is never considered at rest. A particle at rest has linear momentum ZERO and can be anywhere in the space. But, until now, nobody produced a neutrino at rest, while an electron, a proton, a muon, and others, can be set at rest.

    3. The values of the elements of the Pontecorvo–Maki–Nakagawa–Sakata matrix which connect the flavor states of the neutrino with the mass states, are not precise, and experimenters rely on some elements measured in some experiment, for measuring other elements in other (different) experiments.

    Does somebody know whether there are alternative explanations of the neutrino flavor oscillations, without assuming rest-masses for neutrino?

    Kåre Olaussen · Norwegian University of Science and Technology

    Alfredo> I choose engineering

    That is certainly a very honorable occupation, making practical use of the knowledge acquired by physics and its derived sciences over centuries. But I have to respond to a couple of your remarks:

    First: physicists, like engineers, never put theories above reality. Established physics, which on RG is often labelled narrow-minded and dogmatic and ignorant and what not, is established not because of the theories of some theorists (however great), but  because they have been checked and cross-checked and critically challenged over decades. First and foremost  experimentally -- but also theoretically for consistency and alternative explanations. Established physics is established because it constitutes an unbreakable web of carefully verified facts, which also agrees with a framework of theories, methods of analysis, and modes of understanding.

    Second: At the university level at least, it is not always necessary to teach physics as a set of certainties. There are still enough of new physics and phenomena to understand and explore, and "facts" to challenge. However, this is not challenges against the established core of science, but against some parts of its expanding surface.

    Physics, like other parts of science and engineering, develops by building on existing knowledge. Not by tearing everything down, and starting from scratch again according to the current fashion. I am sure engineering is even more conservative and dogmatic in that respect. Otherwise there would be even more court cases in the field. You wouldn't start building bridges according to some Non-Standard Theory of Mechanics, would you?

  • Ahmed Magdy Abdul-Wahed added an answer in Electrodes:
    How can I generate a stable glow discharge?

    Plasma properties:

    • I'm trying to generate a DC discharge in atmospheric pressure:
    • Electrodes: a 200um copper electrode and a steel substrate (large size if compared to the electrode)
    • Gas: is Argon, pumped via a plastic tube with its ending oriented between the two eletrodes
    • Voltage: Up to 500V DC source.


    • The glow keeps turning on and off
    • The current is not constant with time (changes from 5mA to 15 mA)
    • The color of the glow is supposed to be violet for Argon, sometimes it change to golden and the discharge becomes large and emits from the sides of the electrode

    Any suggestions from people who did experimental work with plasma ?

    Ahmed Magdy Abdul-Wahed · University of British Columbia - Vancouver

    Thanks Dr Zekry for these valuable info,

     will try the current source and come back to you 

  • Rosario Caruso added an answer in Papers:
    What are the criteria of determining quality of published papers?

    How can we determined the quality of published papers. 


    Rosario Caruso · I.R.C.C.S. Policlinico San Donato

    Dear Colleague,

    I share below some tools I often use.

    if you want to assess quality of guidelines, you can use the GRADE http://www.gradeworkinggroup.org/publications/index.htm

    if you want assess quality in systematic reviews, you can use AMSTAR checklist http://amstar.ca/Amstar_Checklist.php

    if you if you want assess quality for nonrandomized studies, you can use The Newcastle-Ottawa Scale (NOS)


    Hoping this can be useful for your question.


  • Stefan Paulusch added an answer in Acetic Acid:
    How can I make 2 M or 4 M acetic acid from 100% pure glacial acetic acid?

    Hi all,

    For my plasmid isolation the protocol says to use 2 M acetic acid but our store has only got 100 % pure glacial acetic acid. So how can I make a 2 M acetic acid? Happy for any help!

    Stefan Paulusch · Brandenburg University of Technology Cottbus - Senftenberg

    Hi Erin,

    17.4 M of glacial acetic acid is the value I was looking for. Thanks for helping me!

  • Emil Björnson added an answer in 5G:
    Will 5G be cheaper compared 4G ?

    Will the 5G mobile users have to pay less tariff compared to 4G ?

    We know that 5G offers 100 times higher data rates. Spectrum will be cheaper since it is moving to higher frequency range including millimeter wave band. This should help to drop the costs to 100 times.

    Will it be feasible ?

    Emil Björnson · Linköping University

    5G doesn't exist yet, so we can only make guesses.  Initially, 5G subscriptions might cost more than 4G, so that the telecom operators can differentiate the different services. My guess is that with time the operators will push the monthly cost for a 5G subscription to the same range as today's subscriptions, since most people don't want to pay more than they are already doing. Hence you will get a much better service for your money.

    Huge investments will definitely be needed for 5G. Spectrum will be expensive, irrespective of what kind of bands that will be used. Deployment of new base stations and backhaul infrastructure will also be expensive.

  • Kachy Barrak added an answer in Yeasts:
    Any suggestions on AFM techniques and analysis of yeast?

    Good morning, I have to make a few experiments with the AFM, using a triangular tip, mounted on a cell fluid. On this tip I have to attack the yeast cells.
    How could I do?
    I suggested to use the poly-lysine, but carrying out some tests on a coverslip, do not notice the difference between the negative and positive, on both the yeast adheres perfectly.

    Protocol for the coating:

    - Wash the coverslips with etanole and water and let dry
    - Coating with 0,5ul of poly-lysine (creating of the drops) and allowed to incubate for 15min
    - Washing with water and left to dry for 2 hours
    - Incubation with yeast for 30 min (S.Cerevisiae: 0.05g dissolved in 10ml of PBS)
    - Washing with PBS (3 times)

    Kachy Barrak · University of Bologna

    Hi! thank you for your help!
    A lab member suggested me to use the glutaraldeide instead the polylysine to improve the adhesion of yeast on the AFM tips. What do you think?

  • Viktor Y Butnev added an answer in SDS-PAGE:
    What is the optimum amount of protein that should be loaded on SDS PAGE to exactly quantify it?

    If I load high amount of protein on SDS PAGE and do densitometric analysis (I am using BIO RAD's Image Lab tool) the relative intensity/amount of other bands increases to higher extent than the desired protein. However if I load a low amount, other bands almost disappear giving me higher percentage of my protein. So what is the standard amount that is loaded to do a relative quantification.


    Viktor Y Butnev · Wichita State University

    There is no any standard amount of a protein to do a relative quantitation by densitometric analysis after SDS-PAGE. I would use a low amount of your protein to make sure that other bands almost disappear (in ideal case the other bands reading should be close to the reading of the background, where there is no protein bands). The general rule is that you need to reach conditions where your readings will give you the highest ratio of signal (your band) to noise (background). And always subtract the background reading from your band reading.

  • Peter A. Adcock added an answer in Nafion 117:
    Hello, I am looking for troubleshooting tips for my Methanol fuel cell. Can any one help?

    Hi I am new to alternative fuel cells so I am not sure if I am doing something wrong. I am working with a methanol fuel cell. I have tried 0.1M, 0.5M, 1M and 2M solution of denatured ethyl alcohol. The O2 side is compressed air with a flow rate of 500cc/min. The experiment is being ran at room temp using a syringe pump for the ethyl alcohol and a fuel cell tester for the compressed air. The highest open circuit voltage I can get is 0.3V. My membrane is a  DMFC with Nafion 117, 5 layer and Pt/b on the anode side and Pt/Ru on the cathode side. I have already checked to ensure I placed the membrane in correctly, there are no holes and no damage I can tell.  From the papers I have found I should be able to get at least a 0.8V. I appreciate any help at all, I am at a lose. Thanks

    Peter A. Adcock · Augustana College

    This cell is designed to run on aqueous methanol (CH3OH).  If you are really using denatured ethyl alcohol = ethanol (C2H5OH), you need to switch to methanol (methyl alcohol) to get expected cell voltage.

  • Davis Montenegro added an answer in Electrical Power Systems:
    Why would there be oscillations in node angles while no oscillation in MW in a system observed using Phasor Measurement Unit?

    The phenomenon is shown by around 20 PMUs connected to this grid. How PMUs measure the angle between nodes and I doubt that can cause the error. 

    Davis Montenegro · Saint Thomas University

    The oscillation in power is in fact consequence of the oscillation in node angles.

  • Haitham Hmoud Alshibly added an answer in Organizational Behavior:
    How does national culture affect what happens when an organizational culture is transported to another country?


    Haitham Hmoud Alshibly · Al-Balqa' Applied University

    Thank you my friends for responding to my question to sum up: National cultures differ and organizational cultures often reflect national cultures. Organization cultures, while strong, can’t ignore local culture. Managers can help to be more culturally sensitive by: speaking slowly and in a low tone, listening more, and avoiding discussions of religion or politics.


  • Khalid Hassan added an answer in Variability:
    Can someone help me with my sample size and statistical analysis confusion?

    I would just go to the point. I am having two confusions with my study. Would someone kindly give me information?

    Problem one

    What is the minimum sample size for my model? You can see my model in the picture that i attached here. But here is the description.

    • Predictor Variable: 1 variable with 4 dimensions
    • Moderator Variable: 2 Variables with a total of 5 dimensions
    • Criterion Variable:  1 Variable with no dimensions

    (Please see the attached picture)

    If you can kindly also give the reference. I will appreciate it.


    Problem 2

    The purpose of my research is to find out which among the two moderator variables are the better moderator variable. I only got this purpose after my proposal defense. However i kind of confuse on how i will do that.

    I can find out whether the two moderator variables are significant or not, but how to find out which one is stronger than the other one? Its gonna be obvious if one of them is not significant, but what if two of them are significant? How should i know? Can i use the p_value of each moderator and compare them?

    Those are the problem i am currently facing right now, i hope someone can kindly inform what should do next...

    Thank you and have a nice day...


    Khalid Hassan · University of Diyala

    You can use Gpower software ( avaliable as free version in the web ) to calculate sample size for many types of tests . 

    also, you can get information about sample size calculation from the attacments files

    Good Luck

  • Kuldip Acharya asked a question in Superconductors:
    What is the general formula for calculation of levitation forces in superconductor ?

    Dear all,

    I like to know a general formula to calculate the total force that a superconductor can hold. What are the basic parameters that we need to consider to calculate total force that it can take?

    Answer in detail that easy to understand.



  • Sabine Hahn added an answer in Nursing Staff:
    Does anyone know how to measure the number of nursing staff in inpatient Psychiatry in UK and Norway?

    In Germany, we just generate a new funding system for inpatient Psychiatry. I am grateful for any advice.

    Sabine Hahn · Bern University of Applied Sciences

    Dear Michael

    Not from UK or Norway but from Switzerland :-) How you define good psychiatric treatment or better, good nursing care? What is your outcome variable? Or your quality indicator? There is a lot of literature about grademix. Did you a literature search? I did it in the field of elderly care and general hospital setting. You will find systematic reviews like: Selecting and Applying Methods for Estimating the Size and Mix of Nursing Teams. A systematic review of the literature commissioned by the Department of Health, April 2002. Dr Keith Hurst, Senior Lecturer, Nuffield Institute for Health, Leeds University, 71 Clarendon Road, Leeds LS2 9PL, telephone: 0113 3436985, e-mail <k.hurst@leeds.ac.uk> and more...

    I am not at my office but can send you some articles next week. Ther is also a new book in Switzerland about the topic "Wir brauchen Sie alle - Pflege benötigt Differenzierung. We wrote a chapter about the model we use in our research projects.

    Kind regards Sabine

  • Peter A. Adcock added an answer in Cyclic Voltammetry:
    How does the distance between Ce and We influence CV measurements?

    How does the distance between the counter and working electrode affects the measurement of a cyclic voltammogram? The current has to travel a greater distance. Can it be tha t it does not arrive at the working electrode before I put the next potential?

    Peter A. Adcock · Augustana College


    Is each of those curves repeatable or could part of this be variability from one experiment to another, changing nothing? 

    If your WE and CE are basically planar/flat, are they parallel in all the orientations you tested?

    Compared to the other two, the grey curve is quite odd.  Notice the shift in peak potentials.  If both peaks shift in the same direction it suggests something happened to the reference electrode or perhaps to the working electrode.  If the peaks shift in opposite directions, widening the gap in potential between peaks (giving a curve like the grey one but with upper peak to the right), that would indicate that your uncompensated resistance increased .  The other peaks you display should be proportional to your concentration of electroactive species, provided scan rate is held constant. 

  • José Manuel Gasca added an answer in Bioturbation:
    Can anyone help me with this bioturbation?

    I appreciate any help on this vertical-oblique bioturbation (ichnofossil, trackmaker..). Info: Continental setting (alluvial-coastal plan), Cretaceous, located in lutites overlying a sandstone-microconglomerate level. Thanks in advance!!

    José Manuel Gasca · University of Zaragoza

    Thanks for your useful response Roberto

  • Abdel Rahim Ruby Abdel hamid Hassanain added an answer in Digital Elevation Models:
    How can I download ASTER and SRTM data in heights above mean sea level?

    I need to choose the type of heights while downloading ASTER and SRTM DEM data from Cgiar website 



    Are there another sites useful for this purpose?

    Abdel Rahim Ruby Abdel hamid Hassanain · Benha University

    Dr. Paulo Raposo

    Thanks for adding your answer

    This website wonderful


  • Richard Goodin added an answer in Dissolved Organic Matter:
    Is there any method, technique, and or machine that can roughly measure the alcohols present in a sample of dissolved organic matter/carbon?

    I am trying to identify how much of my dissolved organic matter/carbon consists of alcohol. The identification doesn't have to be precise, I don't need to know all the types of alcohols present, just how much total alcohol is present in the dissolved organic matter/carbon. Just to clarify, the sample is a liquid. Any help would be extremely appreciated, thank you! 

    Richard Goodin · Patheon

    I would use Headspace sampling Gas Chromatography

  • Soma Chakraborty asked a question in Technology Development:
    Could you please suggest me any paper or journal regrading Current state-of-the-art for miniaturized droplet-based evaporative cooling systems?

    This cooling may be droplet water cooling and also the key energy considerations for evaporative cooling system design. Moreover the most  promising areas for technology development in evaporative cooling system can be discussed. 

    Thank You

  • Andrzej Lasia added an answer in Electrodeposition:
    Can anyone give the fundamental theory of electrodeposition in a chemical bath (kinetic equations of ions in the solution, potentiel, current ... )?

    Please find attached a word document in which a cartoon describing the problem is available.

    Final purpose is to orient the hexagonale structure of Te, with any user selected angle theta

    Andrzej Lasia · Université de Sherbrooke

    There are no simple answers! There is a lot of the literature in journals as well.

    Simple and quick answers will always be misleading. One has to study!

  • Nataliya V Roznyatovskaya added an answer in Electrolysis:
    How do I set-up two compartment cell for cyclic voltammetry?

    Can anyone refer to articles on setup for the two compartment cell CV? I have seen "working compartment with working electrode and reference electrode" and second compartment with counter electrode. Another set up refers to first compartment with working and counter electrodes and the second compartment with reference electrode. Which one is it? Is the setup for CV and bulk electrolysis the same?

    Nataliya V Roznyatovskaya · Fraunhofer Institute for Chemical Technology ICT


    If you you use a commercial Ag/AgCl which has a glas frit, but the leaching of chloride still interfere your measurement or you still try to minimize it, you can use a second salt bridge and fill it with your electrolyte, i.e. separate your RE with two salt bridges . However, as far as you use relatively dilute (0.1M) electrolyte, I would prefer a construction called Luggin capillary, as Peter Adcock and Srinivasan Venkatesan have already mentioned it.

  • Thomas Noland added an answer in Chlorophyll:
    What is the relationship between chlorophyll meter readings and total nitrogen content?

    Hello everyone,

    Please help me about nitrogen content in leaves.



    Thomas Noland · Ontario Ministry of Natural Resources

    Numerous studies correlating N with Chl have been done showing a fairly strong relationship. Check out the reference below for a detailed look at this correlation:

    Bonneville M-C, Fyles JW. 2006. Assessing Variations in SPAD-502 Chlorophyll Meter Measurements and Their Relationships with Nutrient Content of Trembling Aspen Foliage. Communications in Soil Science and Plant Analysis.37:525–539.

    The relative chlorophyll content in leaves estimated by the SPAD-502

    chlorophyll meter can be an efficient way to evaluate plant nitrogen (N) status in

    many crops and some tree species. In this study, the SPAD meter was used to look

    for relationships between relative leaf chlorophyll content and leaf nutrient concentration

    in trembling aspen. The variations in leaf chlorophyll measurements were

    also evaluated by using three sampling times and three measurement techniques.

    Hypothetical experimental designs were created to achieve better design efficiency.

    The best representation of overall leaf chlorophyll was found when six SPAD

    readings were taken at different locations on each leaf. There was a positive correlation

    between overall leaf N and estimated chlorophyll content, especially in the top part of

    the trees. Overall, this study suggested that the SPAD meter can give an estimation of

    trembling aspen nutritional status, especially if the differential partitioning of N within

    trees is considered.

  • Abhishek Tiwari asked a question in Abaqus:
    Any documentation for UEL for normal 3d solid element?

    Dear All, can any one suggest me a document describing UEL sample code for normal 3d element, besides ABAQUS documentation :)

    What I need to do is that I need to define a variable based on weight factor assigned to surrounding elements of each element, if there is another way to do it, please suggest.

  • Tristan D. Skolrud added an answer in Ames Test:
    How do I test the results of a translog cost function?

    I estimated the translog cost function (KLEM model) by dropping one equation. now i am to test coefficients. but, as one equation is dropped, in this situation how to perform the test? For example, coefficient qi, (i=K,L,E,M) is zero.

    and i am to test whether  model A is nested in B or not. i use Likelihood values of model  and B. is there any difference in likelihood values when one equation is dropped? If yes, how can i do it? 

    Tristan D. Skolrud · Washington State University

    After you recover the parameter estimates from the missing equation from the restrictions that force the cost shares to sum to one, you can calculate the missing parts of your sample covariance matrix with your estimated parameters. From there, it should be straightforward coefficient testing.

    As to your other question, if you employ maximum likelihood in the estimating process, then the likelihood value should be invariant to the dropped equation (Greene, Econometric Analysis, pg. 278, 6th edition), thus the outcome of any likelihood ratio test you perform will also be invariant to the dropped equation.

  • Amine Bahi added an answer in C57Bl/6:
    Any advice on the transition from adolescent to adult mice?

    At what age are C57BL/6 laboratory mice considered adolescent or fully adults?


    Amine Bahi · University of Nebraska at Lincoln

    Very helpful. Thank you all for your inputs.

  • Shyamal Dutta added an answer in ERDAS Imagine:
    Which of the Image Enhancement techniques should be used before NDVI preparation in Erdas Imagine??

    I am working on Forest Belt of Rarh Bengal in West Bengal, India. Kindly Suggest some measures in this concern.

    Shyamal Dutta · University of Burdwan

    Is Histogram Equlization is necessary in This case?

  • Ashis Ranjan Bandyopadhyay added an answer in Petroleum Refining:
    How can I remove petroleum ether effectively from my petroleum ether extract?

    I would like to know the settings of the machines as well such as for rotavapor: what is the temperature,pressure etc.

    I also have a mivac and would like to know the optimum settings for it.

    Ashis Ranjan Bandyopadhyay

    Rota-evaporator would be the ideal instrument for you. Now your extract will have the solvent and your product. If your solvent is a stable solid (non-volatile), then you can simply remove your solvent at a temperature, slightly higher than that of its boiling point.  At the end you may apply a little bit of vacuum. 

    If your product is a volatile matter, then you problem becomes a bit complicated. In this case the boiling points of the solvent and the product have to be taken into consideration for the conditions to be followed during the separation process.

    Petroleum ether is a mixed hydrocarbon solvent. Various grades of it with different boiling ranges are available in the market. If your compound is a volatile one, depending upon the product's boiling point, you may use n-pentane / n-hexane as solvent .  

  • Alexander T. Morchenko added an answer in Multiferroics:
    Why is multiferroics chosen in spintronic applications?

    Why is multiferroics chosen in spintronic applications?

    Alexander T. Morchenko · National University of Science and Technology MISIS

    Expansion of opportunities of the material property control leads to increase of the spectrum of possible applications, ranging from memory and logical systems to Microsystem technology, in particular, systems for monitoring the health of structures

  • İbrahim Uysal added an answer in Magnetic Separation:
    Is there anyone who can help me with Mg-Chromite separation by Frantz?

    Dear all,

    I am working on ophiolitic chromitites. My chromitites are disseminated, and I would like to separate the Mg-chromite from the silicate matrix. I will do the separation by Frantz magnetic separator. Would you help with the condition of the Frantz to make a successful separation of chromite? 

    Thanks in advance,


    İbrahim Uysal · Karadeniz Technical University

    Thank you Harald, for very detailed information. Yes, I guess Erdi was successful with separation with the condition you offered. 

    Dear Jorg, thank also to you for your attention. 


  • Abhishek Tiwari added an answer in Composite Material:
    What is the subroutine for a nonlocal GTN model?

    Hi, I am working micro mechanical analysis of the composite material by using GTN model. I am encountering the macroscopic and microscopic local phenomenon in the composite is completely depends on the type and arrangement of element. I would like to suppress this mesh dependency of solution in the GTN, could you please let me know is there is any possible method to over this issuse, without using UMAT or UEL. If possible , could any one share their UEL or UMAT code for nonlocal GTN model

    Abhishek Tiwari · Homi Bhabha National Institute

    Dear Mr. Pandi, 

    The answer to your question might be subroutine UEL. 

    From UEL one can call UMAT for local GTN do be done in each element, and then an extra DOF based on weight factor and loacl GTN can be calculated and stored.

    but I need a sample UEL for it for normal 3d elements.

    With regards,