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  • Daniele Spiga added an answer in Dispersion:
    What are the main differences between the following dispersion models: Cauchy, Sellmeier, Lorentz, Drude and Forouhi-Bloomer?

    I want understand, what are the main differences between all these dispersion models, which one is the most precise? In which case? Are there other more innovative and advanced models? Relevant references and links are welcome. Thank you in advance!

    Daniele Spiga · National Institute of Astrophysics

    The Selmaier formula is in general quite accurate, since the coefficients appearing in it are often tabulated. For the Silicon Nitride, for example, the coefficients are reported here:


    However, for measurements in the visible range I have always used conveniently the Cauchy.

    The Lorentz formula is expressed in terms of quantities (e.g. the ratio of free electrons) that are harder to measure/find.


  • Will my IHC slides be okay if I was able to dehydrate them after staining but cannot mount them in permount for a day?

    I'm doing IHC on paraffin sections.  I left my primary antibody on overnight on Friday night and came in Saturday to finish the staining.  When I got to the part where I dehydrate and mount the slides I discovered I don't have access to the room where that's done on the weekend.  I was able to dehydrate them in 95% and 100% ethanol and xylene, but have no access to permount and slide covers.  Will they able okay if I can't mount them until Monday morning? 

    Cheryl Bandoski-Gralinski · The Forsyth Institute

    Thank you!!!  I feel soooo much better :) 

  • Satyabrata Sarangi added an answer in ASIC:
    Do I need to have the basics of Digital Logic to configure FPGA to use it for signal processing application or data communication?

    I want to design a signal processing system using FPGA. I am not sure if I need to revise the basics of the digital logic to configure FPGA to my specific task. I choose FPGA over ASIC for it cheap cost per performance and the flexibility of reconfiguration. However, I am novice to using the FPGA for any application so far. So I wanted a sort of advice from those who had experience with the device.

    Satyabrata Sarangi · University of California, Davis

    Dear Ash,

    Yes, you need to have a strong basic in digital logic before moving forward for FPGA implementation. Because, prior to FPGA implementation you should have a sound knowledge on digital architecture so that you can propose your own architecture for any signal processing or communication related algorithms. Once you are done with your digital architecture, then only you should go for RTL implementation. You should always focus on optimized digital architecture, for which strong digital logic design is a prerequisite. 

  • Andriansyah Andriansyah asked a question in Panel Data:
    Could anyone please provide me with Bai and Carrion-i-Silverstre (2009)'s GAUSS code?

    GAUSS, non-stationary panel data

  • István Lénárt asked a question in Geometric Objects:
    Have I found a new way to the concept of DERIVATIVE?

    Given an algebraic system based on polarities on the sphere. A pair of opposite points and their equator constitute a basic element. (Add the equator to Riemann's unification of opposite points in elliptic geometry.) Two elements determine a resulting element of the same set. This is a partial binary operation with two axioms: ab = ba; (ab)(ac) = a. I call any set of this type a projective sphere. (Cf. Baer's finite projective planes and Devidé's plane pre-projective geometries.) From these axioms a number of important properties can be deduced. For example, if the set has at least two elements a and b, then xx cannot be properly defined for the whole set, because (ab)(ab)=a=(ba)(ba)=b contradiction. This means that in the general case xx must remain undefined, as with the case of division by zero in fields. However, if a smooth curve is given on the sphere, or an oval in a finite set, then the xx operation CAN partially be defined for the elements of the curve or of the oval as the tangent to the given point. Example: given the oval of the four reflexive (self-conjugated) elements in a 13-element finite sphere; the derivative consists of the same four elements. Another example: Given the basic elements on the sphere with homogeneous coordinates. Take the circle with center (1,0,0) and radius pi/4, given by elements (1,√(1-c^2 ),c); its derivative is the curve given by elements (-1,√(1-c^2 ),c). In this interpretation, the derivative does not represent the number indicating the slope of a straight line, but a set of the same type of geometric objects out of which the original curve is made of. Also, this gives that every smooth curve evokes a geometry of its own, defined specifically for the given curve.

  • Ian D Jonsen added an answer in Temperature:
    Could anyone help me with a tool (suggest any effective method) that could be used to assess changes in rainfall variability over a period of time?

    I conducted a survey to assess farmers' perception on climate change and found out that their views on temperature were true on analysis of observed temperature data but views on rainfall were difficult to assess with observed rainfall data. While they think rainfall amount had decreases over the past study period, analysis of rainfall trend does not prove so. I therefore think that, apart from possible increasing trend of PET due to increasing temperature, possible increasing trend in rainfall variability over the period could account for their perception. Hence, I wish to assess rainfall variability trend over the study period.

    Thanks in advance.

    Ian D Jonsen · Macquarie University

    an extremely simple approach to test for an increasing (or decreasing) variance trend, would be to divide your data arbitrarily into 2 parts and use an F-test (ratio of variances). The ratio follows a chi-squared distribution. This ignores the serial dependence in your data but would provide an initial indication as to whether the variance in rainfall has increased or decreased over time. More complicated (but more appropriate) methods to assess how rainfall variance may be changing over time include ARIMA and GARCH time-series modelling approaches (e.g.. see Harvey, A.C. 1993. Time Series Models, 2nd ed. MIT Press

  • A. Rouboa added an answer in Turbine:
    Can any one tell me how to begin with the mean line design of turbines?

    I want to design a radial turbine and I need to know what does the mean line exactly to mean? What is the best way to start? With which documents?

    Many thanks.

    A. Rouboa · Universidade de Trás-os-Montes e Alto Douro

    Dear MA,

    I suggest an interesting book of  entitled "Power System Analysis & Design" of JD Glover et al.

    Good luck,



  • Adam Hughes asked a question in Comsol:
    Are you satisfied with plasmonic simulation solutions?


    I'm trying to perform an honest assessment of the state of open-source software for simulations of plasmonic systems.  For example, simulating the transmittance/reflectance off of an optical fiber with gold nanoparticles on it.  What I'd like to do is get honest sense of how straightforward and accurately such a system could be modeled in commercial software vs. open source.  How big of a disparity in terms of quality and power would you say there is between open source solutions like FDTD Lumerical, Comsol etc... vs. open-source tools for mie-scattering etc...?  Are there clear standouts in terms of open-source plasmonic simulation software that are heads and shoulders above the rest?  How good of an approximation do you expect from effective medium theories vs. brute-force FDTD solvers for modeling biosensors in the lab, and so on?

    If anyone could chime in with their personal experiences, or links to any relevant literature, that would help us a gerat deal!  Thanks

  • A. Rouboa added an answer in Finite Volume Method:
    What are the established solution algorithms for porous media transport equations?

    Such equations are difficult to solver because of heterogeneous coefficients. And due to range of physical processes, the explicit solution usually requires very small time step.

    One good algorithm, we stumbled upon is Multiscale finite volume method proposed by the research group of Dr. Patrick Jenny, ETH Zurich

    A. Rouboa · Universidade de Trás-os-Montes e Alto Douro

    Dear Aachutoch,

    I suggest to read this article (Techniques for Making Finite Elements Competitve in Modeling Flow in Variably Saturated Porous Media of P. S. Huyakorn. 

    Good luck,



  • What is the biggest scientific coincidence that you know?
    For me the two more important are:

    1. The phase transition liquid-solid for the water is that the solid state is less dense.
    2. The dielectric screening in metals is such that the Coulomb interaction among the electrons falls at a distance of the Bohr radius.

    The first one has many important applications as the one of allowing the live in rivers during winter or so on. On the other hand, there are also very interesting electric and thermodynamic phase transitions for this material

    The second, thanks to have a so local electric interaction it allows to have almost free electrons at quite high electronic density in matter and therefore to apply theories so useful as the bands in solids. Over all in metals
    Robin Spivey · Bangor University

    Dear Daniel,

    Thanks for the links. We've discussed the Rovelli paper before and I am indeed aware of Hawking's article. He originally said during a conference in Dublin 2006 that black holes may only have apparent horizons (this year the media got involved). Does this reference to an apparent horizon make sense to you? My understanding of the definition was that if an apparent horizon exists it must be inside/touching an event horizon. No progress then.

    I find all this bewildering, especially as the physics is neither particularly complex nor ambiguous. Could it be that Hawking's mischievous humour is at work? Perhaps all this talk of an information paradox is really some kind of in-joke to do with testing people's gullibility or ability to think for themselves. Might there be a wager concerning how long it takes people outside the upper echelons of physics to see through this nonsense? I understand that black holes were a bit of a joke several decades ago but things have moved on.

  • What is the advantage of a tris-acetate SDS PAGE gel?

    I will be performing a Western blot for a ~350 kDa protein. I have read that tris-acetate gels are recommended for separating high molecular weight proteins. In my lab we pour our own polyacrylamide gels and use a Tris/glycine running buffer. What would be the advantage of purchasing a tris-acetate gel rather than using a low-percentage (6-8%) hand-made gel?

    Jesper Sejrup Nielsen · Aarhus University

    Hi Margot

    No problem with casting your own gels - in my opinion all students should try it sometime... 

    I am not sure this will answer your question but I do know that the pH of Tris/glycine gels can rise to >9 during electrophoresis which can lead to deamination and alkylation. Given the longer running time to separate very large proteins, this may become an issue. As I recall it the pH of Tris acetate gels are closer to pH 7. 

    Hope this helped


  • Determining sample size for in vitro pharmacology experiments?

    My experiments involve subjecting aortic endothelial cells to a specific stress then treating those cells with my pharmacological compound in hopes of seeing a reduction in several proteins. My question involves how would I determine the number of plates and replicates to use. ( I am analyzing lysates and cell culture supernatant) For my dose response experiments I used 8- 12 well plates with half of those plates being control plates and half being experimental plates.

    I have considered using this set up in my full experiments, however once I collect samples from all my time-points, using this method, I will have ~960 invidual samples. This is beyond the amount of samples I can afford to analyze.

    Any suggestions would be greatly appreciated.

    Nikola M Stojanovic · University of Niš

    Well as in in vivo experiments the 5-6 repeats are needed. That is the right thing to do if you want statistical treatment of results later. 

    Try decreasing the number of doses of substances that your investigating from e.g 5 to 3. Or run a pilot study with one dose and if it has an effect in some meaningful concentration  rune few more doses. As for other that are not active just say in paper that the tested dose did not have any effect.

    Hope I helped, all best

  • Mitzi Kramer added an answer in NCBI:
    How to design primer which will pick up different splice variants with Primerdesign for different transcript variants?

    Dear members,

    you all have helped me along very much so far. I have now encountered yet another challenge: I need to design primers for 15 proteins which cover more than one splice-variant of the gene in question (ideally all splice variants).

    As i know so far, Ncbi_Nucleotide lists all known variants and i can pick a primer via the button "pick pimers" for each specific primer. However, findig a primer wich picks up a lot of different splice variants may be just a question of luck and a lot of trial and error in my eyes.

    Is there any programm/website or loophole which could help me along?

    Again, I will deeply appreciate your answers.

    Greetings from Munich


    Ps: Because of this community I could actually get my project going last week. To all members: THANK YOU SOOO MUCH!

    Mitzi Kramer · Ludwig-Maximilians-University of Munich

    Thank you so much for all you answers!!

    They helped me alon a lot!!!

    lots of love


  • How can I find the annotation file of Human HT-12 v2 BeadChip?

    Does any one know where to find the annotation file of HumanHT-12 v2 Expression BeadChip? Only HumanHT-12 v3 and v4 could be found on Illunima's website. Thanks!

    Nick C Wong · Pacific Edge

    I would have thought GEO would have basic platform information which you could download, otherwise I am certain it is in Bioconductor. 

  • Stephen Warren added an answer in Space Time:
    Is the flow of time an illusion?
    This has been discussed on ResearchGate in a rather ad hoc way in relation to another question about the absolute immutability of some physical laws but it really deserves its own separate discussion. Below I summarise the arguments in favour.
    The philosophers
    The nature of time has been the subject of discussion by philosophers for 2000 years or more. In the last two decades their views have crystallised. If time flows - (1) How do we know? and (2) How do we measure its speed? In other words - what frame of reference can we use to measure time?
    The philosophers' conclusion is that they would have to invent another time dimension for the purpose but this would then need a third time dimension and so on ad infinitum. This would be absurd and so they conclude that the flow of time is an illusion.
    Relativity, Einstein and Godel (A World Without Time - Palle Yourgrau - Penguin Books, 2005)
    According to the theories of relativity two observers can never agree on the simultaneity of two events that both witness and neither has a "preferred" position that makes one of them correct. This implies that all events already exist and that what we perceive as the flow of time is an illusion.
    Godel showed that rotating universes were consistent with relativity and proved that in them it was possible to travel back in time. He immediately realised that this implied that the past must still exist and that what he called "intuitive time" is therefore an illusion. In 1949 he published a formal proof that time (in our intuitive sense) cannot exist in any universe. This uncomfortable discovery was ignored for nearly half a century but was revived by Julian Barbour in "The End of Time" and is now widely discussed and accepted by many physicists.
    The Laws of Physics
    The fundamental laws of physics describing the forces are time-symmetric.
    What can we say about the time dimension?
    Time still exists but only as a chronological map in which events are located;
    Time is not in any way like the spatial dimensions because:
    It is anisotropic and contains an entropy gradient;
    If we exist in more than one location in any of the spatial dimensions then we will also always then be in different locations in the time dimension;
    Separations in 4 dimensions are extensions of Pythagoras's Theorem but have the form:
    separation = √[x2 + y2 + z2 - (ct)2], which means that time measurements are imaginary (ict) where i=√(-1), as Hawking suggests in "A Brief History of Time".
    Free will is also an illusion
    We live all our lives all the time but every instant feels like "now"
    Time travel is impossible because (a) there is no dimension in which travel is possible, (b) we occupy all the spacetime of our lives and cannot take back to an earlier time our memories of a later time.
    Stephen Warren · Marlow

    I like this, Andrew!  One of the reasons that philosophers abandoned he idea that time flows is that you cannot measure the speed at which it flows.  This is not just a practical problem but fundamental.  Against what can you measure the speed? We  measure the rate of movement in space against time (dx/dt ) so we cannot use movement in space to measure the speed of time (dt/dx) because the measurements are circular and equivalent to measuring the speed by reference to itself (dt/dt).  We have to hypothesize the existence of another time dimension, t', but then we need another to measure the rate at which t' passes.... and so on ...

    It seems to me that the pursuit of mathematical models has led physicists into a series of mathematical bramble bushes (eg M Theory) from which they can't go forward and can't escape,    I suspect that this is because they (we) do not understand the nature of Time.

  • Molla Hasan asked a question in Free Energy:
    Is there any experimental data on surface free energy of silicon wafer?

    There are few methods to measure the surface free energy of solid surface. For example, Fowkes, Neumann methods. I found lot of data of surface free energy of various polymer surfaces based on these methods. I would appreciate if anyone give me some reference on surface free energy of silicon wafer or some common metals. e.g. Al, Cu etc.

  • Carlos Eduardo Maldonado added an answer in Qualia:
    How to define human consciousness?

    After many years of discussion of the concept of human consciousness, I arrived to the following definition:

    “Conscious processes are qualitative experiences that contain at least four kinds of ingredient:

    a) Sensations and feelings (such as hunger, thirst, happiness, sadness, fear, pain, pleasure);

    b) Perceptual qualities or ‘qualia’ (such as colors, sounds, smells, tastes, etc.);

    c) Cognitive processes grounded on feelings and ‘qualia’, such as attention, thinking, memory formation and recall, etc. and

    d) A spatiotemporal structure, composed of an egocentric spatial framework (according to the work of Arnold Trehub) and a temporal duration of (conscious) episodes of 100 milliseconds to 3 seconds (according to the work of Ernst Poppel)”.

    This definition does not include the controversial concepts of “Self” and “Free Will”.

    I basically agree with David Hume and Thomas Metzinger that the concept of Self is a product of conscious activity, not a metaphysical soul to be considered as a pre-requisite for the definition of consciousness. What is implied by the above definition is the existence of a body that is the bearer of experiences, and also is affected by them. In this sense, the definition is close to the phenomenology of Maurice Merleau-Ponty.

    The feeling of will is relevant for conscious activity, but the possibility - raised by Immanuel Kant - of initiating a totally new causal chain in the world, besides probably being an illusion, is not an essential ingredient of the concept of consciousness.

    The effect of conscious activity on the body (and vice-versa) cannot be explained in terms of Aristotelian “efficient causation” (since it violates the “causal closure” of the world, as pointed by Jaegwon Kim – see link below), but can be understood in terms of “formal causation”, in the sense that the form of body activity can affect the form of conscious activity, and the form of conscious activity can affect the form of body activity.

    Carlos Eduardo Maldonado · Universidad del Rosario

    Dear Alfredo, the danger with Descartes is that he claims a most dangerous dualism, as we all know. The res cogitans, to which you refer, is after all sustained by Descartes' belief in God. Therefore, there is no environment in Descartes work, whatsoever.

    In any case, it seems to be clear, indeed, that our consciousness is to some extent the experience of our environment.

    In other words, please allow me to quote Sartre: we first exist and then we think - if at all. In other words, thinking does not ground the existence. And yes, our existence is an environmental one, as it happens.

    Thank you very much for your comment.

  • How can I increase the specificity of long-tail PCR primers?

    I'm using tailed primers: 20-nt of priming sequence followed by a 10-nt tail. I know to use the annealing temperature (T_A) of the priming sequence (not the full 30-nt sequence) when designing my PCR protocol, but that should only be relevant for the first few rounds of PCR. After that, the tail will have been incorporated into the template, and using the lower, priming-sequence-only T_A will allow for more spurious side products. I'm thinking that after 10 rounds of PCR, I will increase the T_A to that of the full-length, tailed template, to increase the specificity of the reaction. So 10 round at T_A1, 20 rounds at T_A2. Is this solid thinking, or is there a consideration that I am missing?

    Jesper Sejrup Nielsen · Aarhus University

    Hi Brendan

    In my experience the PCR will work just fine by using the lower temperature Tm throughout the PCR.

    PCR is an extremely robust method that very seldom fails. I usually use a standard protocol of 25-35 cycles and a Tm of 55. This works for almost any PCR (exceptions include very long PCRs and repetitive template DNA).

    With that said, your arguments are fully valid and it is always a good idea to try and anticipate potential problems. 

    Good luck


  • Mahfuz Judeh added an answer in Crows:
    Are crows intelligent?

    In common language, some people use the phrase "bird-brains", but this may be very unfair to birds, and show only the ignorance of those people!

    A recent research paper titled, "Crows Spontaneously Exhibit Analogical Reasoning" was published by Anna Smirnova, Zoya Zorina, Tanya Obozova, Edward Wasserman in Current Biology, 2014 DOI: 10.1016/j.cub.2014.11.063.

    Based on this, a general article was published recently- see link! Some excerpts:

    "Crows have long been heralded for their high intelligence -- they can remember faces, use tools and communicate in sophisticated ways.

    But a newly published study finds crows also have the brain power to solve higher-order, relational-matching tasks, and they can do so spontaneously. That means crows join humans, apes and monkeys in exhibiting advanced relational thinking, according to the research.

    Russian researcher Anna Smirnova studies a crow making the correct selection during a relational matching trial.

    "What the crows have done is a phenomenal feat," says Ed Wasserman, a psychology professor at the University of Iowa and corresponding author of the study. "That's the marvel of the results. It's been done before with apes and monkeys, but now we're dealing with a bird; but not just any bird, a bird with a brain as special to birds as the brain of an apes is special to mammals."

    "Crows Spontaneously Exhibit Analogical Reasoning," which was published December 18 in Current Biology, was written by Wasserman and Anna Smirnova, Zoya Zorina and Tanya Obozova, researchers with the Department of Biology at Lomonosov Moscow State University in Moscow, Russia, where the study was conducted.

    Mahfuz Judeh · Applied Science Private University

    Crows are known to be very intelligent. It is not too hard for humans to notice how smart crows are. There is a folktale that crows will gather and decide the capital fate of another crow.

  • Mikhail Pylnev asked a question in Doping:
    How can the absorbance be constant?

    I encountered with this many times. For example, in

    Journal of Hazardous Materials 168 (2009) 253–261


    the authors obtained N-doped TiO2 using different precursors. Actually, the preparation details do not matter. The object is a semi-insulator with the photoexcitation threshold of ~390 nm, which VIS- sensitivity has been enhanced by an impurity N(concentration matters, but there are 3 different levels of doping in the work and the constant absorbance appears even for the level of doping of 0.64 at.% N). The absorption curves(fig.5) were obtained by using the Kubelka- Munk theory from diffuse reflectance measurements. They contain areas where the absorbance equal constant and the areas go right after the Photoexcitation threshold of the undoped TiO2 and to the 800 nm(the region after 800 nm is not shown). I have seen such graphs in other papers, but, I cannot explain it. Why the absorbance = constant there?

  • Carlos Eduardo Maldonado added an answer in Dreams:
    Is active optimism combined with determination sufficient ingredients for the realisation of a dream?

    success stories about people who fulfilled their dreams tell us many things that we might think of as common to most people. Yet, it seems that the recipe has many variations. What are your views? Could you share some interesting stories?

    Carlos Eduardo Maldonado · Universidad del Rosario

    (Ooops! I got so depressed by an anonymous down-vote! Bye dear world!…).

    Just for someone: "moral luck" is concept originally introduced in moral philosophy by B. Williams, and later on developed by N. Rescher.

  • Usama Al-sari added an answer in Falls:
    What is the best way to exclude the effect of casual pathway?

    I am running a logistic regression where the dependent variable is fracture and the main exposure is memory loss, however, other risk factors will be included. But there is a causal pathway (falls) between my dependant and independent variables as people with memory impairment are more susceptible to fall. What is the best way to exclude the effect of falls? Is it possible to adjust the falls variable in my model?

    Usama Al-sari · University of Bristol

    Hi Adrin

    Thank you  for your comment, it was just a mistake with the question. Yes, I mean a logistic regression model. Thanks again.

  • Is the Grid Independency Test (GIT) a must for complex numerical models?

    In complex numerical models having mesh elements nearing a million, its highly impossible for GIT due to time and constraints. So is GIT necessary or is there any alternate option?

    Jonathan R. Binns · Australian Maritime College

    All of the answers above are great, and all necessary.  The problem is always that the order of convergence is never really known, nor whether the solution is monotonically converging or oscillating around a solution.

    Having said that, I will always get some form of rigorous GIT completely, at the very least it shows you the sensitivity to grid refinement around the area of realisable solutions.

  • Jila Torabi added an answer in Constructivism:
    Do you know articles about constructivism approach in entrepreneurial opportunity?

    where is its origin? is this the same with creative approach?

    Jila Torabi · University of Tehran

    Hi niloo

    Thank you dear for kindly answer but absolutely I have them and I ask for more than this articles.

  • Kw Agashe added an answer in Western Blot:
    Level of Phospho gsk3b in western blot?

    I am trying to study the level of phosphorylation in GSK3b in my cell lysates but I cant find the positive control for the PGSK3b anywhere commercially available online. can you suggest what i can use as positive control in western blots

    Thanks for the answer...might try that

  • John Krogstie asked a question in Brain Mapping:
    What parts of the brain is most in use when doing abstract thinking (e.g. developing conceptual models)?

    Find mentioning of the •inferior frontal gyrus and middle temporal gyrus  in  an article in 'Human Brain Mapping'  Neural representation of abstract and concrete concepts: A meta-analysis of neuroimagingstudies  Wang et al. Volume 31, Issue 10. Any other current sources ?

  • Can anyone suggest how I can crystallize the compounds from pet. ether fractions collected by CC?
    I run a column of pet. ether extract and collected 25 fractions from pet.ether: ethyl acetate (80:20) mobile phase. One fraction showed single spot on TLC in same solvent system but difficult to get it as in crystal form. when i concentrate it in reduced pressure it forms green color sticky mass. Can anyone suggest how I can separate it as pure and crystallize form?
    Jacobus Nicolaas Eloff · University of Pretoria

    The next step is to filter the precipitate from the mother liquor, dissolve a known mass in a known volume of a  a volatile solvent.  Then place about 20-50 microgram on a TLC plate and separate the components.  If only one compound is seen with a general spray reagent (unlikely, unless you were very careful) you may have a pure compound.  

    There is another way as well, if your fraction containing only a few compounds is in a glass container and the solvent is allowed to evaporate, there may be small crystals on the side of the test tube or container where the solvent has evaporated.  If you remove the rest of the solution with a pasteur pipette, you may be able to dissolve the crystals that could be relatively pure with an appropriate solvent.  Good luck.

    Usually to determine the structure by NMR MS 90-95% purity should be sufficient. 

  • What is different between N or C terminal Histidine tag for protein purification with Ni column? which one is good for protein purification?

    N terminal or C terminal?

    Olivia Arizmendi · University of Kansas

    It depends on your particular protein, and what are the downstream applications you'll use it for. Some proteins will not fold properly with the His-tag on one side, and some will go to inclusion bodies with the tag in one position vs. the other. In my experience, the N-term is the best to start with. If you run into issues in your downstream application having the His-tag at all (regardless of its position), consider having a thrombin, TEV or another cleavage site in between your His-tag and the protein. Let me know if you have any questions! We purify tons of protein (up to 50-100 mg per preparation), different types of proteins and most are His-tag based.