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  • Abdul aziz Jaafar added an answer in Turbulence:
    Which turbulence model is best to predict reattachment length of flow over a step?

    I have few questions if any one can add to it:

    1. I want to run a simulation with experiments done in free surface water tunnel. Which model you think can predict good reattachment length.

    2. I am using turbulent length scale 6mm and turbulent intensity of 5%. If the reattachment length is not close which parameter should i adjust.

    3. I am using 0 pressure gauge as outlet boundary condition. However experiment was conducted in close recirculating water tunnel. Is it correct? or should i use outflow as boundary conditions.


    Looking forward to hear from you soon.

    Abdul aziz Jaafar

    Dear Hassan

    Just wonder what you mean by reattachment point in your case


  • Mario Radovan added an answer in Ethical Analysis:
    Which influential ethical theorists claim that inter-subjective attunement (sharing affective states with others) is necessary for morality/ethics?

    I'm looking for influential thinkers who argue that intersubjectivity is necessary for being moral and/or living a good life. Ideally I want to find examples of well-known analytic, continental, and feminist thinkers who hold this view. Thanks so much!

    Mario Radovan

    It's me one more time.

    "IMPARTIAL POINT OF VIEW" - there is no such thing! There can be only a consensus.

  • Erico T. F. Freitas added an answer in EDX:
    Are the areas of EDX peaks of different elements in a sample correlated to their percentage abundance?

    I prepared a sample containing C, Mn and O. The peak corresponding to C was much higher compared to Mn and O; yet the percentage abundance (both weight % and atomic %) was found to be lower for C as compared to Mn and O. Can anyone please explain the reason?

    Erico T. F. Freitas

    Hi, EDS analysis is not suitable for seious quantification works for light elements. I agree with previous comments the relative K-alpha peak proportions works for TEM-EDS analysis for thin specimens, when the Cliff-Lorimer method applies, but not for SEM-EDS, when ZAF correction must be used. You should take into account the sample prep issues, and that the interactin volume is different for different elements, being larger for ligher elements. However, EDS quantification for light elements is not precise either for TEM or SEM analysis. The characteristic X-ray signal for light elements are not well defined electron transitions. If you still want to do spectroscopy analysis with high spatial resolution, I would you suggest do TEM-EELS for ligh element quantifications.


  • George Zervoudakis added an answer in Hydrogen Peroxide:


    George Zervoudakis

    As long as:

    a) you have prepared a 40 mM phosphate buffer and

    b) you have a H2O2 stock solution of known concentration

    you can make a dilution of the H2O2 solution with the buffer.

    For example, if you have the usually used H2O2 stock solution of 30% w/w concentration which corresponds to 9.8 M = 9800 mM, you can make appropriate (about 100 fold) dilution with the phosphate buffer in order to obtain a final concentration of 100 mM.

    For a final volume of 10 mL, you need 102 μL of stock solution and about 9.9 mL of the buffer.

    Depending on the final volume of the solution which you want to prepare, you can also make serial dilutions of the stock solution.

  • Kenisha Samantha Russell Jonsson added an answer in Sampling:
    Can someone please assist with a ROC analysis?

    I have data from two samples (community and clinical/service sample) of adolescents who completed psychological evaluations, and I would like to: (1) determine how well the instrument used for these evaluations is able to discriminate between these two samples.(2) to use the ROC analyses to determine the optimum cut-off for differentiating between the community and clinical/service sample. The dataset has 2 other variables: gender and age. Is this information enough to carry out ROC analysis? I attempted this analysis in stata and the AUCs (ranging from 0.518-0.578), seems to indicate that the performance of the scale was nothing more than chance. I am not sure but I assumed for the purpose of my analysis that the community sample is the negative sample( i.e. most likely to be without mental difficulties) and the clinical/service sample is the positive sample (i.e. most likely to be with mental difficulties). Is that correct?  I would be grateful for any guidance on how to implement this model in stata and general advice on model testing.

    Kenisha Samantha Russell Jonsson

    Hi Ronan, Thank you for responding to my request for help.I have now run the Wilcoxon Mann-Whitney and the results suggest that there is a statistically significant difference between the underlying distributions of the psychological scores of the community sample and the psychological scores of the contact/service sample(z = -20.401, p = 0.0000). What is the next move? Can I also ask will it make a difference to the results if one of the samples has over 160,000 observations and the other has only 900?



  • Arnold Trehub added an answer in Cognitive Systems:
    Is Chalmers' so-called "hard problem" in consciousness real?

    In his 2014 book "Consciousness and the Brain: Deciphering How the Brain Codes Our Thoughts" Stanislas Dehaene wrote "Chalmers, a philosopher of the University of Arizona, is famous for introducing a distinction between the easy and the hard problems. The easy problem of consciousness, he argues, consists in explaining the many functions of the brain: how do we recognize a face, a word, or a landscape? How do we extract information form the senses and use it to guide our behavior? How do we generate sentences to describe what we feel?

    “Although all these questions are associated with consciousness,” Chalmers argues, “they all concern the objective mechanisms of the cognitive system, and consequently, we have every reason to expect that continued work in cognitive psychology and neuroscience will answer them. By contrast the hard problem is the “question of how physical processes in the brain give rise to subjective experience … the way things feel for the subject. When we see for example, we experience visual sensations, such as that of vivid blue. Or think of the ineffable sound of a distant oboe, the agony of an intense pain, the sparkle of happiness or the meditative quality of a moment lost in thought … It is these phenomena that poses the real mystery of the mind”."

    Stanislas Dehaene's opinion is "that Chalmers swapped the labels: it is the “easy” problem that is hard, while the “hard” problem just seems hard because it engages ill-defined intuitions. Once our intuition is educated by cognitive neuroscience and computer simulations, Chalmers’ “hard problem” will evaporate".

    Personally, I agree with Stanislas Dehaene's opinion.

    Arnold Trehub


    You neglected the essential point that what all agree upon is an experience of something that does not exist in their sensory world.

  • mohamed abdelshafy asked a question in SAR:
    What is the synthesis and SAR of doxercalciferol?
    • Doxercalciferol 
  • Valentin Loskutov asked a question in Activation Energy:
    What kind of a concentration dependence of the activation energy?

    Dear Colleagues! We are interested in the concentration dependence of the activation energy. For example, the activation energy of viscosity or conductivity of solutions. However, we can not find publications on this topic. Tell me please!

  • Andrey A. Kovalchuk added an answer in Predator - Prey Interaction:
    Where can I find information about predator fish - prey fish - relationships in lakes ?

    I want to evaluate the predator fish - prey fish relationship and its natural variation (without human influences) in some investigated north german lakes. Could anybody give me a good tip? Especially information from northern hemispheric lakes would be valuable.

    Andrey A. Kovalchuk

    Dear Martin, question really wide. I found in my library

    David L.G. Noakes et al. (eds.). Predators and prey in fishes.
    1983, Dr W. Junk Publishers. The Hague. in a momant have no PDF, but will see.

    As well, I'm attaching two books that may by you have, but who knows. Some Chapters their are related with your's question.

    + 1 more attachment

  • Grzegorz Bielec added an answer in Sport Psychology:
    What are the most common tests to measure the motivation for sport in disability?

    I think that  I could use:

    • Physical Activity and Disability Survey (PADS) (Rimmer et al., 1999)
    • BREQ-2 (Markland & Tobbin, 2004)

    Do you Know a better test?

    Grzegorz Bielec

    Dear Miguel,

    Please see the atached paper. I hope it would be useful for you.

    With best regards,


  • Helena Pestana added an answer in Multiple Linear Regression:
    Can anyone tell me what is the maximum number of Dummy variables that can be used in a multiple linear regression model?

    My dependent variable is a scale variable and I have 8 quantitative independent variables. Other than these quantitative variables I have another 5 qualitative variables which i'm trying to include it in the multiple regression model as dummy variables. What is the maximum number of Dummy variables that can be included in a multiple linear regression model?

    Helena Pestana

    Dear all, Inspite i do not agree with all the Murat answer i really do not know why someone vote negative. He gave his best and tried to  help then he should have  "like"

  • Jorge Hernández-Bello asked a question in IL-10:
    Good afternoon, anyone know if there are any database where I can enter a DNA sequence and check which transcription factors bind to that locus?

    I want to know which transcription factors bind to a specific region of the IL-10 promoter

  • Amr Hefnawy asked a question in Zetasizer:
    What is the optimum count rate for accurate DLS measurement of chitosan nanoparticles?

    I am using malvern Zetasizer for the measurement of chitosan nanoparticles loaded with drug.

  • Jochen Wilhelm added an answer in Regression Modeling:
    What is the most appropriate regression model for a response variable that has non-binary values between 0 and 1?

    What is the most appropriate regression model for a response variable that has non-binary values between 0 and 1? Example of a paper shall be appreciated. 

    Jochen Wilhelm

    datatable1 = read.delim("datatable1.txt", sep=",")

    R can handle 37 variables, that's no problem. But you have only 100 rows, what means you have only about 3 values per variable what is really really little. Your model will vastly overfit the data. To get a useful model you should consider irgnoring (most) of your variables or to collect much more data.

    I further have the impression that many of your predictors are categorical variables that seem to be coded by integers (like 0/1 for a dichotomous variable). For 0/1 coded variables this is no problem, but is a variable has more than two levels you should tell R that it is a categorical variable, e.g. with

    datatable1$X3 = factor(datatable1$X3).

  • Hossein Soleimani added an answer in Copolymerization:
    If the percent of third monomer in terpolymer is very low is it possible using copolymerization kinetics?

    Recation follows copolymer kinetic or no?

    Hossein Soleimani

    Monomers are  MMA/BA/AA and AA has low percent

  • Emanuella Fajardo asked a question in Trypanosoma cruzi:
    Does anyone know which Discrete Typing Unit (DTU) the Trypanosoma cruzi Ernestina strain belongs to?

    I can't find this information in the literature.  

  • Areej Zahran asked a question in Palestine:
    How can I calculate sample size for a case-control study?

    I am planning to do a study about the relationship between Body Mass Index and periodontal diseases in Palestine.

    My hypothesis is An increase in BMI will be correlated with an incease risk in periodontal disease.

    There is no previous case-control studies investigated this relationship in Palestine or in the Middle East. How can I estimate my sample size?

  • Walid Ellouze asked a question in Amplicon:
    Primer dimerization problem persists in our qPCR. Checked for contamination and probe primer optimizations but futile. Any suggestions?

    In our qPCR experimentation, we are facing the problem of primer dimerization yielding counts similar to that of samples. We optimized the primer and probe concentrations. We use total plant RNA which is transformed into DNA during the qPCR cycle. The protocol followed for qPCR is 30 min 48 deg; 10 min 95 deg; 15 sec 95 deg; 1 min 60 deg; the last two is repeated 40 times.

    We are sure that there is no contamination; we already checked it several times. Upon loading the gel with these amplicons, no bands are visible through sybr staining for the PCR products. Only primer dimer products are visible on the gel.

    This makes us little confused about the optimization procedure. Hence looking forward to guidance and advice on this subject.

  • Tianyi Li added an answer in Hall Effect:
    What type of sensors can be used to analyze a magnetic flux density on a surface of a sample?

    I am planing to analyze magnetic flux density on a surface of samples. The material will be low alloyed steel with a ferritic microstructure. The range of the magneitc flux density will be lower than 0.2 mT. So far, I used Hall effect sensors. What other sensors can you suggest?

    Tianyi Li

    You can try SQUID (superconducting quantum interference device) if you want to measure it at low temperature. I don't know whether it just makes things even complex. I know someone developed scanning SQUID microscopy which can measure local weak magnetic field, but I don't know whether they have commercial equipment.

  • Muhammad Khattab asked a question in UV-Visible Spectroscopy:
    3D excitation, emission and excitation-emission experiments?

    I am wondering what is the importance and how to interpret these experiments. Also, i noticed that i can't have background corrected (No blank subtraction) for these experiments using perkin elmer equipment. How to solve this problem?!!!! Besides, I appreciate if you could send me some resources to read about 3D experiments.

    Thanks in advance, 


  • Jana Štofilová asked a question in Caco 2 Cells:
    How long can I store Caco-2 cells at -80C?

    How long can I store the Caco-2 cells at -80 degrees celcius. Does anybody experiences about long term (more than 6 months, 1 year, etc... ) storage of the cells in -80C and their recovery? Currently, I don´t have the possibility to store the cells in liquid nitrogen. Thanks.

  • Hashem Moradmand added an answer in LaTeX:
    Do you think Latex rather than Word is more convenient for writing an article or a thesis in psychology field?
    I am undecided which to use.
    Hashem Moradmand

    It is a month I found a software to help computer to be the device to do things faster (in regard to Latex): LYX is a GUI for latex. it is like office and very easy to use and also very stable. 

  • Tianyi Li added an answer in Glass Substrate:
    Will the four point probe give me accurate results about resistivity of cadmium oxide deposited on FTO substrate ?

    my sample is cadmium oxide deposited on Fluorine doped Tin Oxide (FTO) Glass . where cadmium oxide and FTO are electrically conductive .

    how can i measure the resistivity of CdO  without addition from FTO ? 

    Tianyi Li

    My advice would be measure the resistivity of your sample and the resistivity of your bare FTO substrate without CdO respectively. And the resistivity of your sample can be regarded as the resistivity of FTO and that of CdO in parallel. That is based on the assumption that a) your current probes are far enough from your voltage probes so that the current has already distributed between two layers according to their different resistivity; b) your FTO and CdO films are uniform enough so that the distribution of current is also uniform between the two voltage probes.

  • Peter Schaefer added an answer in Acrylamide:
    What is the range of acrylamide concentration in human intestine (gut)?

    Anyone made the studie were the acrylamide concentration in human gut was measured? What is the possible range? Is it in mikrog/ml or rather mg/ml?

    Peter Schaefer

    thank you all

  • James M. McMahon added an answer in Multiple Regression Analysis:
    How do I minimize multicollinearity in multiple regression analysis?

    I conducted multiple regression analysis but I found multicollinearity which leaded to results against my literature. I advised to centering the variable ( X- Mean(X)) but unfortionately regression can not be conducted becuz all variables became constants

    James M. McMahon

    Assuming the question still relates to multicollinearity among the 9 TQM predictor variables for modeling effects on the four outcomes; a critical question to ask is: to what extent are the 9 TQM variables related, conceptually? Are any of them measuring the same or similar constructs. If so, then you would predict, from theory, that the conceptually related variables will show signs of multicolinearity. Perhaps a better strategy before entering all 9 into a MR model at once would be to explore the underlying correlational structure among the 9 TQM variables, by performing exploratory factor analysis (EFA). This would empirically reveal clusters of variables that may be measuring the same or similar constructs. You would then reduce the number of variables to the number of constructs (i.e. factors) represented in the data, by combining them in some way (e.g., generating factors scores using PCA). This would likely solve the multicollinearity problem and be more in line with a sound conceptual hypothesis.

  • Kamal Prasad Adhikari asked a question in Urease:
    What is the mechanism of urease inhibition by nBTPT and heavy metals (Cu and Zn)?

    nBTPT and heavy metal Cu and Zn inhibits soil urease activity and thereby reduces urea hydrolysis.

  • Artur Braun added an answer in Reactor Design:
    What are the main obstacles that could occur when two fixed bed (i.e. trickle bed) reactors are in series or in parallel?

    I am interested to know what will happen if two reactors are operated in parallel (the idea is separate HDO and HC).  Also I was wondering if the operation condition (i.e. pressure and temperature )  in reactor A and B will differ each other.  Can anyone would like to share the challenge of the reactor design? And it possible to separated water coming from reactor A (HDO) prior to second reactor B (HC)?  I would appreciate for your kindness and helpful.  Thank you

    Artur Braun

    Mr. Mponzi, what you suggest there, this is not a Levenspiel Fountain, right ?

  • SOHAIL AHMAD KHAN added an answer in Laminar Flow:
    How do I check which flow characteristic is suitable for tube heat exchanger?

    What experimental data i should take and consider to determine flow characteristics?  Is that laminar flow or turbulent flow suitable for tube heat exchanger?


    It depends upon several factors: fluid being used (in tube as well as shell side also single phase or two phase) in linear direction or cross flow, Reynold number, baffles used, tube layout and its pattern, its use (for refrigeration or boiler) etc. Please see attached some literature downloaded from internet.

    + 3 more attachments

  • Iman (James) Mohammadi added an answer in High Performance Concrete:
    How increasing the cement amount causes decreasing compressive strength of ultra high performance concrete?

    It is mentioned that increasing the amount of cement decreases the compressive strength due to raising the capillary porosity 

    Iman (James) Mohammadi

    Typically the selected cement content should be in the range of 450 to 550 kg/m3, for high-strength grades, such as f'c=65 MPa to 100 MPa. Adding higher than 550 kg/m3 cement contents impacts different performance aspects of concrete including strength reduction and extensive autogenous shrinkage.

    It is proven by the literature that higher porosities results in lower compressive and tensile strengths. Hasselman, Ryshkewithch Schiller and Balshin have provided different models to represent porosity–strength correlation. As a matter of fact, each 10% increase in porosity results in 15% to 25% decrease in strength.

    Capillary porosity and porosity size in general depends on cement particles size distribution, and packing ability of cement. Cement fineness and percent of retain on the 45 ms sieve are factors contributing to this matter, however, in most cases and irrespective of cement particle size distribution, a significant high content of cement in mix-design adds too much fine particles in binder paste which leads to a higher than expected porosity. In such cases substitution a portion of cement with SCMs may benefit mix design, if the early age strength (<1-3 days concrete strength ) is not considered critical !.

    Please find appended some typical mix designs, which may assist you on this matter to justify the appropriate cement content for your mixes.

    f'’c28=65 MPa - 80 MPa
    GP cement=430kg/m3- 460kg/m3
    Ground slag=30kg/m3- 80kg/m3
    Fly ash=70kg/m3- 20kg/m3
    Amorphous Silica=10kg/m3- 20kg/m3
    Fine aggregates 4=669kg/m3- 680kg/m3
    Coarse aggregates=1000kg/m3- 970kg/m3
    Water=178kg/m3- 174kg/m3
    Admixture=4kg/m3- 6kg/m3
    Unit weight=2391kg/m3- 2410kg/m3

  • Jasiel Domínguez Jomarrón asked a question in Coding:
    How I can implement an algorithm for check if a DFS code is the minimum DFS code for a graph?

    I need an algorithm for check if a DFS code is the minimum DFS code for a graph. Thanks