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  • Deviance for binary regression models for expected number of successes smaller than five?

    I have a single response, which denote the number of faulty products/total products (success, or failure ratio) over quite a number of factors (~15). Since these 15 factors are not independent from each other, the number of successes are close to zero in almost half of the cells (combinations of factors). When I perform logit regression, not surprisingly, I find that the expected values of successes in those cells are smaller than five. It is generally known that deviance or Pearson X^2 is close to normal distributed only if E{X} >= 5 (though this is a conservative estimate). However, expected values of quite a number of my cells are smaller than unity! In this case, can anybody recommend me what to do? As far as I can see, there seems to be two methods to deal with the problem:

    1. Construct the model with all the data, find the combinations of factors for which E{X} < 5 (or maybe 3), omit these data and remodel. However, I would not be using some of the data points in (re)modeling.

    2. Construct the model with all the data, but in deviance calculation use only the cells for which E{X} > 3-5.. And for degrees of freedom, use DOF = remaining cells - number of parameters. Here, the problem is I'm not sure whether this is statistically valid, since I would be systematically discarding some portion of the data in deviance calculation, and this may perhaps cause some bias.

    Any help would be appreciated.

    Burak Alakent · Bogazici University

    Timothy, here's the problem in more detail:

    The parts produced are classified as 1 (no fault) and 0 (faulty), hence my response variable is either 0 or 1. These parts are produced under different process conditions (factors and covariates). These conditions may be classified as follows:

    1. Most of my factors (~10 of all variables) are cardinal variables, such raw material types (0, 1, 2, ..6), direction of a manual processing system (L or R), color of the raw material (0, 1, 2), ...

    2. The remaining process variables (~5 of all variables)  are cardinal (continuous) variables, such as mass of the raw material, speed of the rotor, etc. 

    I would like to model the response w.r.t. nominal and continuous variables, i.e. how the probability of success changes w.r.t different process conditions. I am using a logit link (though a loglog link seems to fit better, so I may change the link later). To determine which main factors and interaction terms should be included, I am using deviance (or Pearson's chi square) in addition to Wald statistics. Since deviance statistics is not chi-square distributed if expected number of outcomes is less than five, I cannot use continuous variables directly (and my experience has shown me not to trust Hosmer and Lemeshow test too much). Hence I have discretized the continuous variables, such as mass flow rate is divided into four ordinal variables (0,1,2,3), each representing a different mean flow rate. Hence I've ended up with 15 factors, at two to five levels. For each of the combination of these levels&factors, I have determined the number of parts produced, and the non-faulty ones among these produced.

    So, here's the problem. I have approximately 7500 observations, but since 15 factors are highly correlated (experimental results are not obtained from a factorial design, but a real process), each cell corresponding to each level of 15 factors does not contain, or contains only a number of parts. For example, at a flow rate of level 0, machine direction left, color 1, etc, there are only 2 observations. If, at the end of the logit model construction, success probability prediction for that cell (combination of factors) comes out to be 0.5, then the expected number of non-faulty parts would be 1. Now, to evaluate the performance the model, I would like to examine the deviance statistics, but the deviance statistics is over all the cells, including those for which expected number of successes is smaller than five. At this point, what should be statistically valid strategy? That's what I'm trying to ask. I can think of two solutions:

    1. During modeling, neglect combinations of factors, for which there are only a very small number of observations.

    2. Include all observations in the model, but during deviance calculations, neglect combinations of factors, for which there are only a very small number of observations. This one seems to me a better choice, but I'm not sure whether I'm violoting something related with Deviance statistics.

  • Roman V. Gulyaev added an answer in XPS:
    What is the necessity of using Gaussian Lorentzian mixed function while describing the XPS data of any material ?

    I have carried out XPS analysis of CNFs/ACF samples to know the nature of C1s, O1s spectrum. I have often seen that people use mixed Gaussian Lagrangian function to interpret the results. What is the necessity of doing this? 

    Thanks in advance.

    Roman V. Gulyaev · Boreskov Institute of Catalysis

    Dear Bhaskar Bhaduri, first of all,

    could i classify some meanings within your question? 

    The shape of the photoelectron line. It represented by a convolution of 1) core level lineshape 2) instrumental broadening. The last factor consist in 2.1) primary radiation energy distribution convolved by 2.2) analyser broadening

    I begin from the tag.

    2.2) Analyserl broadening is Gaussian. Almost always. 

    2.1) Primary X-ray radiation. In the case of characteristic primary radiation (X-ray tube)  - it is Lorentzian. The physics of that is the same than the Lorentzian lineshape of 1) Core level.

    Besides, Lorentzian core levels takes plase in the insulators or seniconductors. In the case of metals, or semimetals, in general, in conductive materials, the core-level lineshape is described by Fano resonanse profile. In XPS it describes by Doniach-Sunjic function. It originated from the interaction of a photoelectron with its "onetime place" in atom. This interation is "rather simple" in the case of inconductive matreials, but delocalized electrons "spoils a picture" in the case of conductors, which is leads to assymetry in the core level lineshape. 

    So, in the case of C1s line from sp2-hybryde carbon (semimetal, conductor) the lineshape will be describes as a convolution of DS-function * Primary radiation distribution * Analyser function. where the * - convolution. 

    In the case of sp3-carbon (insulator) the lineshape will: Lorentzial core-level * Primary radiation distribution (Lorentsian, as a rule) * Analyser function (Gaussian) = Lorentzian*Gaissian = Voigt functiom ~ (very close to) pseudo-Vougt function.

  • Iván Sanz added an answer in Swine Influenza:
    Can you answer my questions on genetic and antigenic characterisation of the influenza virus?


    1- Q: I work on the swine influenza virus, I want to know if the results of the genetic characterization of the virus are sufficient to get an idea on the mode of evolution, or is antigenic characterization is necessary for the HA protein
    2-Q: HI test, I understand the concept, but I want to know if the main objective is to know the presence of the cross reactivity
    thank you  

    Iván Sanz · National Influenza Center, Valladolid

    Hi Zeineb,

    1Q-I think genetic characterization can´t be alone without antigenic assays. They are different things and can give you high level complementary information if you do both techniques at the same time. In the topic you are talking about, Genetic characterization can gives you a virtual frame of what is happening with the genes in your virus, but if you want to test the characteristics and behaviour of your viruses, you have to test by antigenic too. Think about you have a virus in wich you can see a mutation. If you can´t culture it, you will never know if this virus have potential ability to infect humans, or in your case swine.

    2Q-Probably the first objective of HI assays is the surveillance of vaccine effect. We usually do in our National Influenza Centre serological test using HI assays to test vaccine effect in general population with pre and post vaccinated sera of each individual. This can give us an image of the global protection status of this population, and the protection offered by the vaccine each year. With this concept, we can check the vaccine failure if the vaccine composition have a missmatch with the influenza circulating strains (in this topic is very important the antigenic characterization). Of course also can be used to test cross immunity process.

  • Francesc Codony added an answer in Qualitative PCR:
    Does anyone have experience in validation of qualitative PCR assays?

    Need examples of "applicability" and "practicability" parameters evaluation

    Francesc Codony · GenIUL


    maybe a quick read of this doc could be a good starting point


    best regards

  • Universe is static!!! Yes or no?

    Space of Universe is static! Yes or no?

    Question: Are there any observations that do not fit into the model static space of Universe, are there any theoretical obstacles to the existence of such a model?

    I assume that the Universe is eternal, infinite and static, it is not expanded and not curved, it is possible to construct a preferred inertial frame of reference in which the CMBR is most isotropic. The matter in this space evolves, but the average density of matter and energy (in large enough volumes) fluctuate within a rather broad range.
    The light in this model is "tired", the speed of light depends on the optical density intergalactic medium. Gravity is also "tired" t.i. weakens a little faster R2. The energy of destroying matter goes into the surrounding vacuum. The excess energy from the vacuum give rise to new particles of matter.

    I state that all the observed cosmological effects can be explained in such a Static Model of the Universe.
    See attached "Basic_Cosmological_Formula_1_En.pdf"

    Dear colleagues, I do not ask, what are the problems faced by other theories (though I would be interested in your opinion on that. The General theory of relativity is not applicable to the entire space of the Universe).

    Erkki J. Brändas · Uppsala University


    I guess Christiaan Huygens discussed plane and spherical waves without taking the square root of the Hamiltonian. In fact the latter is indeed straightforward by writing Maxwell’s – or the Klein-Gordon Equation as a matrix problem.

    Anyway do not get upset by this comment. However, I am concerned about your evaluation of the pioneer physicists as being bipolar, insane, crazy, autistic, etc. and then taking this as a basic insight and explanation that they must be wrong in their thinking.

    I think, as already said, that your problems originates in your belief that “everything” are EM waves and therefore must obey Maxwell’s equation.

    De Broglie conveyed the simple insight that the photoelectric effect pointed to the particle properties of light (despite zero restmass) and wave properties of the electrons (with non-zero restmass), which was later unequivocally verified in the Davisson-Germer experiment.

    Another consequence was of course that viewing the electron as a matter wave explained Bohr’s quantization assumption, i.e. that the number of wavelengths must fit the condition that the angular momentum must be an integer multiple of Planck’s constant.

    Since the Lorentz transformation, as I have showed above, can be derived without any reference to light or electromagnetic phenomena, de Broglie’s understanding infers no puzzle that should cause you worries, viz. “why can I derive de Broglie’s wave length for an entity with mass, with speed 𝜐, from the Lorentz transformation, which automatically results from the Maxwell’s equation, with the implication that the matter wave must be an electromagnetic wave”.

    Although Galileo's discourse between Salviati and Simplicio is great reading reflecting Galileo’s great insights, we know now that he did not anticipate non-circular orbits and did not provide the correct theory for the tides. In these pre-Newton times he should not be criticized for this although Kepler’s proposal of an elliptical orbit for Mars was known during his lifetime.

    Anyway, for me “”the beef” is an entity with nonzero restmass. With Maxwell’s Equations you will not even get the bun!

  • Keith Henry Nicholls added an answer in Devonian:
    Can anybody help me in identyfing a Devonian fossil?

    The fossil in the picture was found in the Upper Devonian carbonates in the Daisy Lake, Sudetes Mts, Poland. Does anybody know what it might be?

    Thank you in advance 

    Keith Henry Nicholls · University of Chester

    Looks very much like the Lower Carboniferous rugose coral Lithostrotion - would be younger than generally anticipated

  • Ersin Karataş added an answer in Oxalates:
    How can I produce recombinant ENZYME ?

    I need to produce Oxalate decarboxylase enzyme as a recombinant enzyme. I choosed my source organisim named bacillus subtilis 168 designed my primers (with doubt) and I want to express in pET-SUMO vector. Are there anyone who tried this vector to produce protein for enzymatic reaction ? OR Can you please suggest me a vector system to produce protein for enzymatic reaction ?

    Ersin Karataş · Bezmiâlem Vakif Üniversitesi

    Lorriane clark; I have pET-SUMO expression system and so I also have DE3 competent cells

  • Has anyone successfully detected HPV16 E7 by using the cervimax kit on formalin-fixed paraffin embedded human tissue samples?

    There are a couple of papers which show the use of this kit on such samples, but we haven't been able to make this kit work on our CINII samples. We have tried the solutions provided in the kit for antigen retrieval and other generic antigen retrieval methods with the antibody but none worked. The tissue always come out with background, when compared to a secondary only control. Does anyone have any suggestions? Also, please note that this kit was purchased 3 years ago but didn't work at the time it was bought either. 

    Cristiano Teodoro Russo · Pontifícia Universidade Católica do Paraná (PUC-PR)

    Hi Megha,

    have to be in tissue? you could not use samples in liquid-based cytology?

    The kits: PreTect ™ HPV-Proofer, Norchip AS, Klokkarstua, Norway and NucliSENS EasyQ®, BioMerieux SA, France, works well for this.

    It is also possible to use OncoTect ™ HPV E6, E7 mRNA Kit of IncellDx, which uses the technique of flow cytometry. I will use this in my research.

    I have helped.

    Best regards

  • Temim Deli added an answer in Ear:
    How can I run a gel on gDNA extracted from rat ear punch?

    I need to run a gel before sequencing it. What percent gel should I run it on, and what size ladder is addecuate?

    Temim Deli · Universität Regensburg

    Dear O. Marte,

    You have to pay attention for the scientific jargon used in your question as it is so critical for scientists to understand you question aim when reading it: Genomic DNA is run on a gel and not the inverse case. Also, it is the DNA that is targeted for sequencing and not the gel!!!

    Anyway,  usually the genomic DNA ranges from ~30 to 50 kb in size. For this, a low agarose gel concentration will do (i.e 0.8 %), you may even use 1 % or 1.5 %. It will not really matter for such kind of electrophoretic migration, unlike smaller DNA fragment when you have to increase the gel concentration (restriction fragments analyses for example). Personally, I don't use the marker for the case of Genomic DNA, but this will be necessary for PCR products (quality assessing). However, if you feel the necessity of ladder use, you may include a molecular weight markers from 10 kb to 50 bp in length.

    Good luck!

  • Louis Brassard added an answer in Cultural Analysis:
    Is the `culture´ concept a way of setting distance between Humans and other animals or it can be a bridge for inter-species comunication?

    Some scholar debates are around whether or not can we define culture as a trait present in many non-human animals, or if it´s just an exclusive human trait.

    The importance of this particular barrier comes not only from the obvious issue of culture as the basic frame for developing and explaining humanity as unique, wich is not my main interest.

    I suggest that by establishing the presence of culture in other species, and performing cultural analysis method  of the later, we can open new ways of inference and knowledge in our own.


    There are certainly uniquely human type of cultures and I also agree that the difference between non-human and human culture is that human consciousness is a mammalian consciousness which is splitted between a regular mammalian awareness of the here and now and theatrical narrative consciousness. An human can immediatly distinguish when another human act for doing actions or act as an actor, a play intended for an audience.  I think this capacity is the critical capacity that lauch a particular tribe of primate on the cultural path towards the human tribe.   I follow Mithen in the Singing Neanthertal, that it began with a new type of leadership in some primate tribed based on a singing dancing practices for emotional control.  I think that this cultural leadership practice has allowed a conscious access to what I call the self-enact control room which existed in mammals and more developed in primates but which is mostly unconsciously access for sensory-motor integration of the mammalian action control in the here and now.  What was implicitly used could then be used to access to the fundamental narrative decomposition of behavior in order to culturally construct behavior in narrative world.  I can elaborate but I will stop the story there.  

    In de oratio to the dignity of Man, Giovanni Pico della Mirandola said:

    At last, the Supreme Maker decreed that this creature, to whom He could give nothing wholly his own, should have a share in the particular endowment of every other creature. Taking man, therefore, this creature of indeterminate image, He set him in the middle of the world and thus spoke to him:

    ``We have given you, O Adam, no visage proper to yourself, nor endowment properly your own, in order that whatever place, whatever form, whatever gifts you may, with premeditation, select, these same you may have and possess through your own judgement and decision. The nature of all other creatures is defined and restricted within laws which We have laid down; you, by contrast, impeded by no such restrictions, may, by your own free will, to whose custody We have assigned you, trace for yourself the lineaments of your own nature. I have placed you at the very center of the world, so that from that vantage point you may with greater ease glance round about you on all that the world contains. We have made you a creature neither of heaven nor of earth, neither mortal nor immortal, in order that you may, as the free and proud shaper of your own being, fashion yourself in the form you may prefer. It will be in your power to descend to the lower, brutish forms of life; you will be able, through your own decision, to rise again to the superior orders whose life is divine.''


  • Pradip Kumar Singh asked a question in Fellowship:
    Can anyone educate me about "Carl R. Woese Postdoctoral Fellowship Program" ?

    what is procedure?

    And  where u can use this ?

  • Holly Tran asked a question in HEPES:
    Where can I order 1x DNA oligonucleotide annealing buffer?

    Specifications: 10mM Tris-HCl, 50mM NaCl, 1mM EDTA, pH 7.5-8.0

    I've tried looking into IDT but their buffers contains HEPES.

  • JC Spender added an answer in Money and Banking:
    How is the increasing presence of what Marx defined as interest bearing capital distinct from other social forms credit?

    What significant role does this play in real as opposed to fictitious accumulation of capital?

    JC Spender · Kozminski University


    Indeed, by definition.  

    To David's question, I am sure Marx would have been amazed and enthralled by Stephen Marche's piece http://lareviewofbooks.org/essay/literature-second-gilded-age/

  • Chris Hsiung added an answer in Lentivirus:
    Could we use the DH5alpha instead of Stbl3 for lentiviral plasmid transformation and cloning?
    I will perform some transduction with lentivirus produced in our lab (not commercial made). At Addgene they say that the plasmid that I've got should be transfomed into Stbl3, however I was wondering if i could used the DH5a strain. Anyone has any similar experience?
    Chris Hsiung · University of Pennsylvania

    In our lab we frequently prepare retrovirus and lentivirus plasmids in DH5alpha. We have not identified any problems with recombination and the viruses certainly infect just fine for our purposes, though we have not compared side-by-side with a Stbl3 strain. So certainly DH5alpha can be used productively.

  • John George Hardy added an answer in RGD:
    Why can't MSCs attach to an RGD modified PEG system?

    Hello, I added thiol RGD peptide into PEGNB polymer and after UV-photopolymerization, MSCs are seeded onto 2D hydrogel. However, the cells can not attach to the RGD-modified surface and there is no migrating at all after 24 hours. Instead, the cells form aggregates and remain alive. Has anyone done this before?

    Thanks for any reply!

  • Vincent G Guida added an answer in Bivalvia:
    Does intracellular digestion of larger food particles (like it can be found in bivalvia) occur in teleost?

    I am especially interested in ingested particles of a particle size from 1 to 10 μm. Are food particles of this size range normally processed by intracellular digestion in teleosts?

    Vincent G Guida · National Oceanic and Atmospheric Administration


    Thanks for the clarification.  If the digestive system of a fish is not adapted for taking in 1-10 µm food particles from the plankton, it is not likely to take in any sort of particles of that size from any source.  Of course I may be totally wrong...but that's how science works sometime...finding out why the reasonable answer is not the right answer.


  • Can anyone help me with troubleshooting of a Cary 100 UV-Visible spectrophotometer (Varian)?

    The software is not able to establish a connection with the hardware. The scan mode is offline.

    Alexandra Müller · Ruhr-Universität Bochum

    Is the instrument connected to the computer via a network cable? If so, have you checked the network connection? I'm not sure if this applies to your instrument, but I had a similar problem with another machine. The computer didn't recognize that the instrument was connected by a network cable. If this is also true for you, deinstallation and rebooting of the network adapter may help. 

  • How can i adjust ultrasound intensity?

    i have an ultrasonic piezoelectric without any valid datasheet and i need to adjust it's intensity to the low one type.  what parameters should I notice about?!

    Behzad Vaziri Hassas · University of Utah

    Sorry I just wrote the DIMMER as dimer.

    U can definitely use dimmer and it is quite cheap. you can reduce (control) the output voltage of the dimmer that goes to the piezo..

  • Atanu Pati added an answer in Prisons:
    Can anyone share his/her studies on the sleep-wake profile of the prisoners?

    We are planning to write a project with the objective to examine sleep-wake profile of the prisoners. I want to know if anyone can share his/her experience on similar or comparable studies on the prisoners?

    Atanu Pati · Pt. Ravishankar Shukla University

    Dear Dr. Zeitzer, Thanks for the input. Please send me your publication/s on sleep study in prisoners. I would appreciate receiving PSQI, PSQI-A, MAPI. We are planning to study sleep-wake profile in prisoners of Chhattisgarh in India. We will definitely seek appropriate ethics clearance before initiating the study. Thanks, Dr. Dina Gojkovic.

  • Paul Germann added an answer in Stress:
    Do you believe all active substances increase in stress conditions?

    we have some examples which indicate active substances( percentage and yield/m2) increase in normal condition., but generally, active substances are increased under stress condition.

    Paul Germann · AbbVie

    Kinder stress conditions organisms are focusing in the most important biological principle: Survivals, this means systems which supports survivl offen the species Are supported in'lower' Organismus while survival ob the individual are supported in 'high er' organism, where reproduction is more demanding. This is influencing the balances ob the substances

  • Bernard Desroches added an answer in Nietzsche:
    Is Western nihilism the result of reduction of Western symbols of human dignity and virtue to consumption slogans?

    Nietzsche's Zaratustra  introduced moral nihilism in Western Europe. His arguments were recuperated by ideologies that denied the achievements of the Enlightenment such as freedom and equality for all citizens. These virtues are symbols of human dignity for every man and woman. However advertisement reduces these human values to slogans urging citizens to consume and to put on their identity a normative set of substitute consumption goods. Is this after all the victory of Zaratustra's nihilism? (see attachment)

    Bernard Desroches · University of Lyon

    Two themes are crossed.

    Dear Callaway,

    What kind of mediation or third term would here be possible ? I really wonder.

    For instance, whith the First French Republic (that one of  1789 to 1791, because it will be different as soon as 1792), history works (for instance Yannick Bosc and Droit naturel teams and researches)  attest that what we call "catéchismes révolutionnaires" - numerous small books, often few sheets, written in quite a number of original exemplaries, laid down by everybody or almost at the time (bakers, teachers, preasts, members of the Constituante et cetera, farmers... men and women, everybody) - all say the same thing : Liberté (and what it is), Egalité (and what it is) et Fraternité (and what it is). This is for me the Republic, in three words (whith their 'contenu') - and since 1905 we even have a fourth one, which is "Laïcité". Those three words are not a 'slogan', they are a _motto_.

    I surely would not tell an American what is Liberty. He knows. But as for the others - first components of Republic...  Apparently, capitalism is compatible whith liberty (liberalism), capitalism is compatible whih equality of rights (Sate of Right), but this is here unsufficient. Equality of rights do not guarantee the possibility of brotherhood. There is no brotherhood possible whitout hypocrisis between M; Bernard Arnault and myself, because the condition of life of M. Bernard Arnault has not much to see with the ones of me.  I claim that Equality of rights must be verified by what I call "equality of condition" (to define precisely, but the expression makes senss). Anyway _this_ is an objection to the compatibility of capitalism and Republic : no brotherhood is possible or this is an hypocrisis.

    You refer to the terms of current politics, but in terms of general politics, the equation is not the same, I mean. I much too long.

    Best regards

    To Carlos Eduardo. Thank you very much. As a matter of fact my thesis is entitled "Aphorism as a philosophical object". I did read Nietzsche, by the way. I naturally see that aphorism is not at all a slogan (which is very depreciative, in french semantics).

    Aphorisms I refer to, to begin with, are Hippocrate's ones. Then Beckett's, then Karl Kraus's one's. Two hundred authors in my thesis.

    Best regards

    B. P. J. Desroches


  • Nisha Rizvi asked a question in Perforant Pathway:
    How to best detect pre- or postsynaptic mechanism using paired-pulse protocol in rat hippocampal CA1?

    To test pre- versus postsynaptic mechanism of drug action, I am using the paired-pulse protocol. I am curious about the rationale behind altering Ca2+/Mg2+ ratio to better detect small changes. Can anyone help? How does increasing or decreasing this ratio affect PPR? I would love to know the mechanism (residual calcium hypothesis etc) behind it. Also how would this relate to synapses that show control paired-pulse depression like the medial perforant pathway in DG?

    Thank you


  • What is the number of possible non-isomorphic trees for any node?

    Does anyone has experience with writing a program that can calculate the number of possible non-isomorphic trees for any node (in graph theory)?

    Sudev Naduvath · Vidya Academy of Science & Technology

    What do you mean by the term "non-isomorphic trees on ANY VERTEX?" If you mean binary trees or rooted trees, you may refer certain books on GRAPHICAL ENUMERATION. The first suggestion is GRAPHICAL ENUMERATION by F. Harary (Academic Press, New York).

    There are certain other materials in this area which seem to be useful for you are downloadable/viewable in the following links.



  • Amir Emami asked a question in Magnetics:
    Are non-integer magnetic moment materials, half metal?


  • Marimuthu Sivakumar asked a question in Coating:
    What will be the effect when coating NiO on LiFePO4, Will it affects the lattice parameters? If so, why?

    LiFePO4 has been prepared using polyol process (245deg.C), NiO coating has been done at 500 deg.C.  In this case, will it affects the lattice parameters? If so, why?

  • Abbas Rahdar added an answer in Magnetization:
    What are the conditions of magnitude of Ms and out-of-plane crystal anisotropy for a thin film to have no in-plane magnetization?

    What are the conditions on the magnitude of Ms and out-of-plane crystal anisotropy for a thin film to have no in-plane magnetization?

    Abbas Rahdar · Zabol University

    Dear Kai,

    Very Thanks.  i am experimentalist

    All the best,Abbas

  • Francesc Codony added an answer in Proteolysis:
    How can I check wild wine-yeasts proteolysis?

    I want to test my isolated wild yeasts strains for proteolytic activities. Can you recomment a methodoly, which is easy and quick, for screening purposes in the lab?

    Thank you!

    Francesc Codony · GenIUL


    In classic bacteriology the proteolytic activity from some bacterial strains is often measured by their gelatinase activity. May be you can consider the Gelatinase test as a simple and cheap approach.

    Take care with the medium pH and the optimal pH growth of your strains.

    best regards

  • Oliver Serfling added an answer in R:
    What resources or books (free or otherwise) do you use for R?
    It will be useful to create a collection of R resources here. Please provide links for any free resources or citations for books and a brief explanation.
    e.g. http://www.r-bloggers.com/ - A blog aggregator for posts about R.
  • Hamed Haghi added an answer in Flotation:
    How can we depress kaolinite clay to improve flotation gold recovery?

    we have gold in pyrite ore, we extract this gold by flotation, but some time we have with our ore kaolinite clay which interfere with gold in flotation and give and give us bad gold recovery.

    Hamed Haghi · University of Tehran

    Hello dear Mostafa;

    I have some solution for you?!

    1) please check PSD of clay in the slurry and check presence of gold in fine particle size ranges (in order to avoid  gold loss prior floatation); in this case you can use hydro-cyclone clusters for clay (particles normally finer than 0.02mm) removal prior flotation; it is normal good way; in overflow stream you have clays and you can feed cyclone underflow stream to flotation cells. If you need accurate hydro-cyclone system for fine particles removal like clay; I am collaborating with well-known brand for supply of hydro-cyclone with very fine cut-size.

    2) if you can not use hydro-cyclone for clay removal; you should use good depressing and dispersing agent such as Sodium Silicate in order to avoid entrainment of Kaolin during frothing.

    Please don't hesitate to contact me in case of any further questions;