ResearchGate Q&A lets scientists and researchers exchange questions and answers relating to their research expertise, including areas such as techniques and methodologies.

Browse by research topic to find out what others in your field are discussing.

Browse Topics

  • Susan Taft added an answer in Titania:
    Could Richardson's Law be the basis for the initial electron transfer to the metal particles?

    It has been suggested that Richardson's Law could be the basis for the initial electron transfer to the metal particles during high temperature reduction from the (reduced) titania substrate discussed in the attached paper. I would appreciate any thoughts regarding this.

    Susan Taft · Independent Researcher

    The original paper was published on the open website arXiv.org in condensed-matter/material science topics.

  • Luis Briseño-Roa asked a question in Cell Viability:
    Efficient way of stripping / removing CD markers?

    Hi everyone. Does anyone happens to know an efficient way of stripping / removing cluster of differentiation (CD) markers from the surface of cells - yet keeping cell viability? Many thanks. 

  • How can I cope with a degenerate multivariate normal distribution?

    I am studying a multivariate normal (MVN) model for inference on graphs. Due to the topology of the graph, the covariance matrix is singular by construction, resulting in a degenerate MVN. Due to this, I cannot use maximum likelihood estimation, since I cannot obtain the inverse of the covariance matrix. What is the best course of action in such a situation?

    Anselmo Ramalho Pitombeira-Neto · Universidade Federal do Ceará

    Your comment seems reasonable. I will be more precise: In my MVN model, the mean is a linear combination of a parameter lambda, so that \mu = A \lambda, where A is a m x n matrix with n > m. The covariance matrix is S = A diag(\lambda) A', where ' denotes transposition and diag(.) is a n x n diagonal matrix. It happens that A is not full rank, so that S will be singular. A naive approach would be to eliminate dependent rows of A, so that the modified A will be full rank, and S will be non-singular. However, I am afraid that, by doing this, I am somehow losing information contained in covariances among the elimated dependent rows and independent rows.

    The best so far I have come across on how to tackle this problem is the following section of a Wikipedia article:


  • If I prepare a new (unknown) composite material as supercapacitor/pseudocapacitor, then what should be its potential range for CV curve?

    As per my knowledge it should be  +-0.5 V with respect to the open circuit potential. but in practice it is not true. please advice.

    Subbukalai Vijayakumar · University of Ulsan

    we can extend the potential up to 1.2 V for aqueous electrolyte but oxygen evolution reaction starts at particular potential that affects the stability of electrode.  

    Hence, the potential range should be selected in order to avoid the oxygen evolution reaction.

  • Dr.K.Mophin Kani added an answer in BOD:
    What are the factors that can influnce DO, COD and BOD in groundwater?

    I want to describe water quality data that contains DO, COD and BOD parameters, among others.

    I accept with Arif but some of the things i wish to added to it; naturally without any pure air circulation within aquifers and groundwater table, the possibility of the presence of DO is nil in almost all ground water or aquifers; there is high degree of the presence of COD since the presence of natural elements present in that particular area. probable BOD level will be minimum if there is no organic inputs; if there is a presence of organic inputs and the BOD level too measured with high level.

    factors responsible for these things were; nature of that place, substratum, soil type, natural leaching, nature and type of aquifer, atmospheric pressure, permeability of soil and rocky substratum and so on.,,

    wish you all success 

  • No colonies after transformation in E.coli BL21 de3 cells. What to do?

    I successfully cloned a gene and checked it by colony pcr and restriction digestion. There after i transformed the construct in E.coli DH5alpha for plasmid prep and isolated sufficient amount of plasmid whose quality has been checked through agarose gel electyrophoresis.

    When i tried to clone the same expression construct in BL21DE3 i am not getting any colonies. 

    My results are-

    control A- competent cells bl21de3 plated on LB without antibiotic- got lawn of bacteria

    Control-B competent cells bl21de3 transformed with pEt23b null vector- a lot of colonies are visible0-0 transformation successful

    Actual Transformation-competent cells BL21de3+PET23b based construct- got no colonies.

    Antibiotic used is ampicillin and  concentration in plates are 50ug/ml .

    Help me to sort out the issue.

    Vishal Srivastava · Indian Institute of Technology Delhi

    i used Qiagen spin mini prep kit for purifying plasmids so i dont think it should have chances of phenol or etanol. As i mentioned above the plasmid is working fine in case of DH5-alpha...

  • Elmar Buchner added an answer in Sedimentary Basins:
    Can anyone give us the reasons for absence of hydrocarbons in Kufra Basin, Libya ?

    Most of the Libyan sedimentary basins contain hydrocarbons except Kufra Basin. Can anyone give us the reasons for absence of hydrocarbons in Kufra Basin ?

    Elmar Buchner · Hochschule Neu-Ulm

    A very detailed compilation of the evolution and the hydrocarbon potential of the Al Kufrah Basin was recently published by Daniel P. LeHeron et al (2014): Early Palaeozoic evolution of Libya: perspectives from Jabal Eghei with implications for hydrocarbon exploration in Al Kufrah Basin. I attached the publication.

  • Stephen Ball added an answer in Zetasizer:
    How to prepare sample (Carbon nanotubes) for particle size determination using Zetasizer nano.

    Since carbon nanotubes are insoluble in water and are needed to be dispersed for effective determination of particle size, What is/are sample ways of preparing such a sample?

    Stephen Ball · Malvern Instruments

    The problem with CNTs and DLS is that they have a tendency to "clump" together and dispersing them into single particles is very difficult. However, we have been able to measure the length, diameter and chirality of CNTs in a single experment using the new Zetasizer Helix instrument (which combines DLS with Raman spectroscopy). The white paper below describes this in more detail, and includes information about the sample preparation steps required to produce a stable dispersion of individual nanotubes.

    Hope this helps.

  • Should I use probit or dprobit regression?
    I am doing a regression on a dependant dichotomic variable "accepting civil marriage contracts or not". Should I use probit or dprobit regression?
    Jose María Martínez-Rioja · International Center for Tropical Agriculture (CIAT), Palmira, Colombia.

    If you're talking about Stata commands, they're "technically" the same. However, from my humble opinion, it would be preferable for you to use the «probit» routine, and then the «margins» or «mfx» command. Although some effects might not be statistically significant at some values of the information vector, they might by signifficant globally. Hence, it would be preferable for you to study the results in two stages: Probit, defining which are the globally relevant regressors, and then execute an analysis of the marginal effects at the vector values of interest.

  • Magali Durand added an answer in Cryogenics:
    How do you calculate the cooling capacity in cryogenic chamber dimension?

     On cryogenic companies I can see different capacity 20 W, 100 W, 150 W.

    Magali Durand · University of Central Florida

    Thanks you.

    We ordered our cryocooler and after that I suppose you just have to test to adjust.

  • Claude Miller added an answer in Risk Perception:
    Can anyone recommend risk perception scales for measuring adolescent and young adults reactions to film stimuli (short movies)?

    We are building the capacity to conduct a study about risk perception with test persons aged 16-24 years. They will be exposed to short films under different pre-conditions (different cognitive frames we'll prepare them with before watching).

    Claude Miller · University of Oklahoma

    Hi Henrik, you might use and/or adapt items from the Youth Risk Behavior Surveillance System (YRBS) survey developed by the Centers for Disease Control and Prevention (CDC, 2013) http://www.cdc.gov/HealthyYouth/yrbs/index.htm 

  • Mohammad Afzal added an answer in Ectopic Pregnancy:
    Is consanguinity a risk factor for ectopic pregnancy?

    Consanguinity is a risk factor of many of common and rare diseases. Is ectopic pregnancy is also one of them?

    Mohammad Afzal · Aligarh Muslim University

    We donot have any account of consanguinity and ectopic pregnancy in any study in india or elsewhere. If it is so somebody can point it out.On the other hand incompatability due to some heterozygosity with blood groups can be lessened due to inbreeding as happens incase of Rh factor.

  • Sleman Bsharat added an answer in FPLC:
    How can I improve my protein read in SDS PAGE?

    My protein has a size of 170KD with a MBP tag at the N terminal. It's purified from insect cells. Right now I can get a quite sharp peak (it actually includes 1.5ml elution volume) after FPLC column. But I still can see multiple bands show up on SDS PAGE, and I can see a lot of aggregation on the negative stained sample using TEM. Is there any way I can improve? 

    Sleman Bsharat · Technion - Israel Institute of Technology

    may your protein isnt 99% purified and you have some protein that elute with them and make aggregation ??? i suggest to do ion exchange and or to change your pH of your  change elution buffer

    also you can to do mass spectrometry to this strange bands ,and you will identify the bands identity 

  • James F Peters added an answer in Robotics:
    What are applications of convex sets and the notion of convexity in mathematics and science?

    In a Euclidean space, an object S is convex, provided the line segment connecting each pair of points in S is also within S. Examples of convex objects in the attached image include convex polyhedra and tilings containing convex polygons.  Can other tilings containing convex shapes be found?

    Solid cubes (not hollow cubes or cubes with dents in them) and crescent shapes (a partial circular disk containing all points inside the disk) are also examples of convex objects. Except for the 3rd and 5th cubes, the cubes in the attached images are convex objects (all points bounded by walls of each cube are contained in the cube).


    From left-to-right, the cresent shapes are shown in the attached image are convex: Nakhchivan, Azerbaijan dome, Taj Mahal, flags of Algeria, Tunisia, Turkey and Turkmenistan. For more examples of crescent objects, see


    Can you identify other crescent shapes in art or in architecture that are convex?  Going further, can you identify convex objects in art or in architecture?

    The notion of convexity leads to many practical applications such as optimization


    image processing


    and antismatroids, useful in discrete event simulation, AI planning, and feasible states of learners:
    In science, convex sets provide a basis solving optimization and duality problems, e.g.,
    Convex sets also appear in solving force closure in robotic grasping, e.g.,


    Recent work has been done on decomposing 2D and 3D models into their approximate convex components. See, for example, the attached decompositions from page 6 in
    J.-M. Lien, Approximate convex decomposition and its applications, Ph.D. thesis, Texas A&M University, 2006:


    There are many other applications of the notion of convexity in Science. Can you suggest any?

    James F Peters · University of Manitoba

    Dear Daniel,

    Many thanks for your observations.   Do you have any examples of intractable problems that have been approximated using the notion of convexity?    One thing comes to mind about how one might solve the approximation problem.   Try J.M. Lien's approach, where we allow we relax the convex set requirement and allow shapes to be partially convex.    There are many examples showing partial convexity in


  • Does measurement error only imply the error incurred by the measuring equipment?

    Does measurement error only imply the error incurred by the measuring equipment?

    Ana Isabel Janeiro · University of Lisbon


    Your Error Measurement is the sum of your all procedures you have undertaken before the analysis (sample preparation) and the error of  the measurement in the equipment of course.

    In many cases the more significant error is the last one and you can use the precision as your measurement error.  There are many ways to calculate the precision and it is easy to find in the literature.

    It depends of the  method you are using .  

  • Hey! I am using a PZT crystal for generation of Ultrasonics. What is the volatge and current ratings I have to follow?

    I am using them for flow measurement of liquid. ( These sensors are of negligible thickness and less than 1 centimeter in diameter)

    Krzysztof Herman · Wroclaw University of Technology

    Dear Vasuki,

    it depends what kind of vibration mode You want to use (a thickness resonance or a radial one). You can easy have an equivalent circuit measuring U an I along frequency.

    As for the voltage and current used the main idea is not to let the transducer to exceed Curie temperature bacause of depolarization. If You work in a pulse mode You can apply short bursts or short pulse (Dirac delta) of hundreds of volts and expect a current in a range of  a few ampers.



  • Mauro Torsello asked a question in Gold Nanoparticles:
    How to define fixed-rigid atoms in GROMACS?

    I'm trying to model gold nanoparticle with a rigid gold core and i found that in the paper "Simulation Study of Aggregations of Monolayer-Protected Gold Nanoparticles in Solvents" J. Phys. Chem. C 2011, 115, 18991–18998 the authors are able to use fixed gold and sulfur atom positions using gromacs. I looked on the web but i didn't find something related to this topic. Is it really possible to deal with rigid body in gromacs? I already tried constraints but I get several errors. Thanks

  • Henrique Zingg asked a question in Failure Analysis:
    Can anybody help me with the failure analysis of Drucker-Prager´s criterion?

    I'm having a little problem with understanding why  this criterion is not able to represent a proper response at a triaxial stress state. The criterion is defined with the second invariant of the deviatoric stress tensor. 

    Could anybody please explain me this?

    Thanks in advance!

    Best regards,


  • Lev Goldfarb added an answer in Machine Learning:
    Machine Learning vs Pattern Recognition?

    Among the AI courses there are two important courses called  "Machine Learning" and "Pattern Recognition". Apparently  much of the stuff covered in ML is also found in PR.

    I want to know what are the main differences?

    Thanks in advance.

    Lev Goldfarb · University of New Brunswick


    Please don't ask questions as to " a formal definition of " any field, because such "definitions" do not and cannot exist. This is not a good sign. ;--)

    (Even mathematicians have never attempted a formal definition of their field.)


    To some extent I agree with you. But I strongly disagree regarding:

    "And the ambiguity is not necessarily a problem either."

    The main problem with the emergence of ML outside PR is that this fragmented the field and the basic efforts without offering any fundamentally new insights into the basic problem. And this is what creates the present confusion

  • Christopher R. Moore asked a question in Climate:
    What is the estimated calendar year ranges for Bond Events 1-8?

    Bond Events 1-8  are indicated as 1400, 2800, 4300, 5900, 8200. 9500, 10300, and 11,100 kya, but I don't see anything that indicates how long each of these climate events lasted.  

  • Adil Salman added an answer in Simulink:
    Can anyone show me how to build a simple model of Redox flow battery in Simulink?

    Can anyone guide me how to build a simple model of Redox flow battery in Simulink?

    Adil Salman · University of Nottingham

    Simulink is an Integrated tool in matlab with the help of which one can do modelling and simulation by using the simulink blocks available for different fields of study.

    I know some basics of redox flow batteries but the thing is i want make a simple model of redox flow battery . i have read several papers but most of them have done some chemical related mathematical modeling which i don't understand.

    if you can help me in understanding of some basic mathematical equations for redox flow batteries so that i can model it in Matlab/Simulink.

  • Can anyone help with a TALENs based knock-out construct?
    TAL1 length 20

    TAL2 length 20
    Should I consider my TAL length as 20 or 40 (TAL1+TAL2)?
    TAL1 binds to +strand while TAL2 binds to -strand of the DNA.



    How to proceed for the steps 2a and 3a (I have pasted below):
If the TALEN length is 12-21:

    2a. Pick plasmids for the RVDs 1-10 (e.g. pNI1, pNN2, pHD3, pHD4….) +
destination vector pFUS_A

    3a. Pick plasmids 11 up to N-1 + destination vector pFUS_B#N-1
(pFUS_B plasmids are labeled B1-B10 but they are used for RVDs 11-30 – if the 
RVD #N-1 is 19 or 29, use the same destination vector pFUS_B9)
    Here is how I intend to proceed:
    For the first 10 RVDs (of TAL1) which has the sequence:
    I will select for first 10 RVDs of TAL1 as below:
    pHD1, pNI2, pNI3, pNI4, pNH5, pNI6, pHD7, pNI8, pNH9, pNG10 + destination vector pFUS_A
    For the remaining 10RVDs of TAL1, I should use:
    pNH1, pNG2, pNI3, pNH4, pNI5, pHD6 pNI7, pNI8, pNH9, HD (Nothing for this 10th RVD, as per step 3a: Pick plasmids 11 up to N-1?) +pFUS_B9 ??

    Similarly for the TAL2 whose RVD sequence is:
    HD HD NI NI NI NI NG HD NG NH NH NG HD NH NG NI NH NI HD NH+ destination vector pFUS_A
    I will use for first 10 RVDs of TAL2 as below:
    pHD1, pHD2, pNI3, pNI4, pNI5, pNI6, pNG7, pHD8, pNG9, pNH10
    And for the remaining 10 (of TAL2): only 9 has to be selected as 10-1=9?)
    pNH1, pNG2, pHD3, pNH4, pNG5, pNI6, pNH7, pNI8, pHD9, NH (None for this 10th NH?) + pFUS_B9 ??

    But the protocol does not talk about the Right arm RVDs?
    Puneet Prabhakar Singh · The University of Edinburgh

    The procedure is straight forward. Follow http://www.addgene.org/static/cms/files/Golden_Gate_TALEN_assembly_v7.pdf

    Is, you have to design two separate TALE ; Right and Left. But you can do that simultaneously. Follow the same protocol for both.

  • Pseudo random bit geberation
    "For an application, I have to generate 10K pseudorandom bits from a user-supplied password (8-16 characters). What are possible options? Which one do you recommend and why?"
    Alireza Jolfaei · Griffith University

    Your question is not clear. What kind of properties are you looking for? Long period, speed, security,....??? What is your application?

    You can use Mersenne Twister which is, by far, the most widely used PRNG, and use a small lagged Fibonacci generator or linear congruential generator  to feed it.

    you can also use a symmetric cipher, such as  AES or salsa20, to generate a pseudorandom sequence.

  • Luigi Grassi asked a question in Resins:
    O Boc carbonates lability to piperidine

    As a byproduct of my synthesis I might have a N,O Boc protected Thr, on resin, which for the next steps needs to be kept capped.
    The resin is subjected to a 6h treatment with 70% Pip in DMF, to free the phenolic OH from the Boc which surely reacted in presence of DMAP, to afford the corresponding Phenyl-Boc mixed carbonate-ester. Would this treatment even cause the unwanted deprotection of the above mentioned alkyl OH on the threonine, from the Boc? thanks to everybody

  • Arjyabrata Sarker added an answer in Likert Scale:
    How best can you analyse likert scale data using SPSS

    Please help me with a step to step approach.

    Arjyabrata Sarker · Jahangirnagar University

     It's a long way...you should get some help practically who can perform you the desired tests practically. You can use few SPSS manuals for basic understanding, but the point is software using is a practical matter, theory is something different from it.

  • How can you chemical bind the stearic acid with the TiO2 particles in the paint?

    I need to chemically bind TiO2 particles with stearic acid and it should not washed away or not vaporized by heat. That's why chemical bonding need. I m try to prepare the hydrophobic paint using Stearic acid, please help me

    Andre Luis Araujo Parussulo · University of São Paulo

    Serguei do you know any paper that show the increase of adsorption of stearic acid with UV radiation?

  • Gregor Witte asked a question in Chromatography:
    Booking system for instruments

    Hi all,

    I am looking for a (if possible) freeware system to manage bookings for our various instruments. It should provide the following features:

    - groups of instruments (like e.g. chromatography systems, biophysics, robotics, ...), but some of the instruments might be in two groups simultanously (example: an analytical size-exclusion chromatography systems with MALLS can also be used for small-scale preps, thus it needs to be visible in "chromatography" but also "biophysics")

    - fast calendar overview for all systems in one instrument group (...see if there's a free chromatography system in the next days)

    - easy booking (click & go in the calendar)

    - statistics (user-wise and also research group wise - to obtain the percentage use for each participating lab)

    - logbook for each instrument where the users can note problems or leave notes for the next user

    - for selected instruments:

    the respective person in charge of the instrument has to agree that the person booking it is really allowed to book it. However, it might be easier to only let the responsible person do the booking for these things then.

    I've checked quarzy - but the statistics for instrument use can only be done per user - not per associated group (AFAIK).

    Any suggestion is highly welcome.... thanks......gregor

  • Can we run panel cointegration with the help of SPSS and/or STATA?
    If not, then please suggest a software to run panel cointegration.
    Jose María Martínez-Rioja · International Center for Tropical Agriculture (CIAT), Palmira, Colombia.

    The two commands on Stata in this topic are «xtwest» and «xtpmg». First one tests panel cointegration, and latter estimates non-stationary heterogeneous panel models. Both of them must be installed, since they're not included automatically on Stata SE or Stata MP.

  • Osamiabe Ignatius Enodiana asked a question in Lakes:
    Is anyone familiar with comprehensive difinition of lake pollution with sitation

    what is lake pollution,sources of lake pollution,effect of lake lake pollution,management and control of lake pollution.and which statistics can one use in analyzing lake pollution