Q&A

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  • Can we find the reduction or oxidation kinetics of any metal using UV-VIS spectrometry?

    Can we find the reduction or oxidation kinetics of any metal using UV-VIS spectrometry?

    Matthew R Mills · Carnegie Mellon University

    Another consideration is how clean the conversion is.  If the spectral changes go from the original spectrum to the final spectrum with clean isosbestic points, and you know the extinction coefficients for each species it is possible.  This also assumes that your oxidant or reductant does not have any absorbance in the region where the spectral changes are occuring.  

  • What do you think of the "health" of the Capital Asset Pricing Model?

    The CAPM is based on a robust theoretical framework, but empirically demonstrated weakness. The beta does not seem to be the only factor that can explain the risk-return relationship. Do you really think that the CAPM is dead?

    Theodore C. Moorman · Baylor University

    Even if dead, it could still be useful and has led to a number of innovations.  Consider that most people look at a market index to get a quick idea of how their portfolio is performing.  Also, look at the explosion in market index funds and how most mutual funds are compared to a market index.

  • Could anyone suggest an investor that could be interested in funding of poultry vaccine development?
    We are interested in seeking for a grant to fund/complete our project in poultry vaccine development. Could any one kindly suggest a related outlet allowing applications from international institutions? Any help with relevant links/contact or other forms of assistance will be appreciated.
    Faruku Bande · Putra University, Malaysia

    Thanks Ben, very interesting!

  • Is it best to place a radiation measurement lab on the 4th floor or in the basement?

    You want to establish a radiation measurement lab. You also have the option of choosing either the basement or a top floor (say 4th floor). The lab is supposed to be capable of measuring all types of environmental radiations.  What would be the best option?

    m s Vishnu · Bhabha Atomic Research Centre

    Basement is preferable for environmental radioactivity measurements considering background reduction , shielding constraints and ambient temperature. But not suitable for a place having potential to flooding. 

  • John E. Mindur added an answer in Trypan Blue:
    How can I avoid cell death when restimulating T cells for passive EAE ?

    I am trying to perform adoptive transfer in EAE models using MOG(35-55) in B6 mice, but always got many dead cells after 3 days of restimulation invitro. For example, I start culturing 5x10^6 lymph node cells and splenocyte in 1ml RPMI medium (24 wells) containing 50ug/ml MOG. After 3 days, when counting cells with trypan blue, I found that most of the cells had been damaged, and when using the lympholyte M to separate dead-viable cells I only got 10^5 living cell in which CD4+ T cells only account for 20-30%. This mean that I have to use a lot of cells and peptide If I want to inject 5x10^6  CD4+T cell into the recipient. So can anyone give me a good suggestion.

  • Is it possible to neutralize all the positive resistances in a circuit by an equivalent negative resistance?

    I have asked this question with two purposes - first, at the request of Barrie Gilbert to terminate the irrelevant discussions in the question below...

    https://www.researchgate.net/post/whats_the_real_behavior_of_rc_circuits

    ... and second, to answer the question of Erik Lindberg asked at the end of this discussion.

    In the discussed arrangement (an RC circuit with various leakages), there are three resistances in parallel - R, Rc and Rv, and the equivalent resistance is Re = R||Rc||Rv. My idea is to connect a variable (N-shaped) negative resistor in parallel to Re and begin adjusting its resistance RN. Depending on its value, it will "eat" some part of Re and it will dissapear (become infinite):

    1. RN = Rv (Rv is neutralized) or RN = Rc (Rc is neutralized)

    2. RN = Rc||Rv (both Rc and Rv are neutralized)

    3. RN = Rc||Rv||R (all the positive resistances are neutralized)

    In case 2 (a load canceller), I think we should obtain a perfect exponential shape... and this should solve the leakage problem.

    The next my idea was that if we continue decreasing this "destroying" negative resistance beyond this point of exact leakage neutralization, it will begin "eating" a part of the positive resistance of the "useful" resistor R... and finally, it will destroy all the resistance R. This means that the resistor R as though already has an infinite resistance... and behaves as an ideal current source... Actually, this is the idea of the Howland current source and its special case here - Deboo integrator. But while in the classic Deboo integrator the negative resistor (INIC) neutralizes only the positive resistance R, here it neutralizes all the resistances in parallel (the useful R and harmful leakages).

    So, my question now is, "What happens if we try to neutralize all the positive resistances by an equivalent negative resistance (case 3)?"

    My doubt is that, as a result of this 100% neutralization, this circuit will become unstable, and if the negative resistance begins dominating over the equivalent positive resistance, the effective resistance (the result of the neutralization) would become fully negative. And here, I suppose, the voltage across the capacitor will begin self-increasing in an avalanche like manner...

    The same problem exists in the Wien bridge oscillator... and it is solved there by applying a non-linear negative feedback in the INIC... Maybe it is possible to keep the circuit stable in a similar way?

    Pisupati Sadasiva Subramanyam · Vignana Bharathi Institute of Technology

    Dobromir Dobrev's method of injecting opposite currents at the two terminals between which the positive Resistance is connected ,I am afraid, leads to no current through the Resistance and is as good as Open circuiting or Switching off the Circuit.

    By connecting in Series an Equal Negative Resistance amounts to short circuiting the Resistance.

    In that case if it is a circuit having D. C Source with only Pure Inductance (having neutralized the resistance of the coil) finally short circuits the Voltage Source. If it is a Pure Capacitive Ckt.  the Capacitance gets charged fully Impulsively and acts as Open circuit for D.C.Supply  If it is LC series Ckt. with D.C. Source there will be no  current flow at all , since  L acts as O.C. initially. and C acts as O.C.finally.(Time Constant RC = RL =0 since R = 0 the Capacitor gets charged Fully Insantaneously - Impulse Charging)

    In the case of A.C. Source the circuit will act as Pure Inductive ckt. or  capacitive ckt or LC series circuit or Series Resonance Circuit,depending on the Values of L and C if connected alone or in Series when all the Resistance values is Neutralized.

    P.S.

    .

  • What can explains the positive relationship between trade and relative demand for skills in developping countries?

    Many empirical studies have found strong evidence for the existence of positive relationship between trade liberalization and relative demand of skilled to unskilled employment in developing countries.

    The question that need more investigation is how to explain this positive relationship?

    Abdulrazzak Charbaji · Université de Technologie et de Sciences Appliquées LIBANO - FRANÇAISE

    We have to very careful in interpreting the sign and magnitude of any simple relation between two variables.  A simple relation between two variables is said to be spurious and we better elaborate the simple relation by  explicitly  bringing  in  other variables into the multiple regression or multivariate or structural equation model  and determine the true relation after partialling out the effect of other variables.  As an example, if you compute the simple relation between trade and relative demand for skills in developing countries  using Time Series Data then, you ma end with a positive relation between the two variables because the two time series data grew over time. That is why testing for stationary, cointegration and VEC or VAC Models become imperative in this case.

  • How can I calculate a well depth for an atom such as Selenium?

    Actually, I want to calculate well depth for selenium atom and I have only its Vander Vaal radius and covalent radius. I am not getting how to calculate the well depth.

    Md. Arifur Rahman · Case Western Reserve University

    Use AFM

  • Voltage or current controlled device is a BJT? And what does "voltage controlled" and "current controlled" mean? Is this a property of the BJT?
    This discussion is old as the very bipolar transistor... but it is still interesting...

    In my opinion, a BJT can be controlled either by voltage or current depending on the situation. If we want a maximum gain (the case of amplifying stages), we apply a small (to be a linear device) AC voltage (e.g., ±100 mV) with an additional appropriate DC biasing voltage (e.g., 0.65 V) directly to the base-emitter junction; then we can consider the BJT as a voltage-controlled device. The problem is that the base-emitter junction, like a diode n-p junction, is not so suitable for a voltage control since it behaves as a voltage source (more precisely, as a constant-voltage nonlinear "resistor"). Figuratively speaking, there is a conflict between two constant-voltage devices connected to each other (an incorrect arrangement). The dual incorrect arrangement is if we try to inject a current into the BJT collector (the "dynamic load" odd idea).

    If we want a maximum input voltage range, we drive the BJT base-emitter junction through a resistor Rb (the picture in the attachment below); then we can consider the BJT as a current-controlled device. We may look at this arrangement from two viewpoints. First, we can think of the combination "Vin + Rb" as a simple current source that is shorted by the transistor input (the base-emitter junction acts as a current load). Second, we can think of the combination "Rb + base-emitter junction" as a transistor with a large voltage range (a voltage load).; as though the transistor has enlarged many times its input voltage range and it has transmuted into a kind of FET-:) The increased linearity will be an additional advantage...

    This is an old V-to-I technique widely used in the measurement in the past - imagine an old-fashioned analog voltmeter built by an ammeter (a movement) and a resistor connected in series. Like in the case of the BJT above, we can control a real ammeter by a small voltage (a few hundred mV). The only difference will be the linearity...

    But yet, what does "voltage controlled" and "current controlled" mean? Is this a property of the input source or of the very BJT?
    Lutz von Wangenheim · Hochschule Bremen

    @Vaibhav Bharatrao Vaijapurkar:

    1.) For RE=0 the circuit does work, of course, but it has a very poor stability against temp. variations.

    2.) It is a known fact that we have ac feedback only in case of CE=0. However, DC feedback does always exist - independent on CE.

    3.) Therefore. it is logical that the input resistance increase can be observed only for CE=0 (In all of my replies I never have mentioned CE at all !).

    4.) The Early effect describes an Ic increase due to VCE increase (identical to VCB increase) for IB=const. Hence, we conclude that IC variation is due to an increase in the electrical field across the pn junction). And the field is produced by the voltage.

  • Henry E. Schaffer asked a question in Personality:
    How do a remove a person from the list of co-authors because this person isn't a co-author (but has same first initial a a co-author)?

    I tried to do this from my "Account" page - and don't see a way.

  • Curt Nielsen added an answer in Yeasts:
    Is there any other way to induce the GAL1 promoter in yeast PJ69-4A without using raffinose?

    I actually inserted my target DNA in pYES2/NT B vector and transformed in yeast PJ69-4A, and want to express my target protein in yeast PJ69-4A. 

    I still haven't received a satisfactory result.

    Curt Nielsen · Evolva Holding

    For academic research, there are many strains, which can be used. Classical strains include W303 and s288c. The s288c was used in the yeast genome sequencing project and yeast genome deletion project. For academic research the BY strain series from Euroscarf (http://www.euroscarf.de/) in Germany, is very commonly used and they can be accessed for the shipment and handling fee. In addition, the FY1679 background can be used (also available from Euroscarf). Just remember to go for the haploid strains. You could also by a strain from ancompany selling the expression vector you are using.

    Feel free to ask if you have any further questions.

  • Maryam Mirdamadi added an answer in Fish:
    Can anybody help me to identify a fish of the Exocoetidae family?

    It was obtained by a fisherman in Tumbes mangroves. I have pictures, videos and formolized animal.

    Maryam Mirdamadi · University of Tehran

    1. pectoral fins high on sides, greatly enlarged

    2.lower lobe of caudal fin longer than upper lobe

    3.lateral line low

  • Why feedstock viscosity increases at higher mixing speed?

    I prepared feedstock varying speed from 35 rpm to 51 rpm. I found feedstock viscosity decreases as speed increases within 35 to 43 rpm. But after 43 rpm, viscosity increases with the increase of speed. What might be the reason behind this occurrence.

    Md. Arifur Rahman · Case Western Reserve University

    Can depend on the type of feedstocks and temperature of processing. What type of feedstock are you using?

  • Casey Kneale added an answer in Alkylation:
    How do I perform alkylation of indole NH of harmine hydrochloride salt using sodium hydride and alkyl bromide?

    I want to alkylate indole NH of harmine hydrochloride salt with methyl bromoacetate and sodium hydride.

    Any suggestions on how to neutralize the indole NH hydrochloride salt and use it for the alkylation using sodium hydride as base?

    Casey Kneale · California University of Pennsylvania

    I would like to state that I made an error in predicting the regiochemistry of this reaction in my previous suggestion. I somehow over-looked the nucleophilicity of the deprotonated indole. I have attached a publication citation which contains this information as well as experimental procedures to prepare a variety of alkylated harmine derivatives via NaH and alkyl halides. As stated above nuetralizing/deprotonated harmine hydrochloride can be easily done with any weak base, even sodium carbonate. pH 10. The material is pretty hydrophobic and will precipitate from solution, but could benefit from an extraction. A solvent such as ethyl acetate should be fine.

    Synthesis and structure–activity relationships of harmine derivatives as potential antitumor agents. Rihui Caoa,Wenxi Fanc,Liang Guoc.European Journal of Medicinal Chemistry. Volume 60, February 2013, Pages 135–143. doi:10.1016/j.ejmech.2012.11.045

  • What might cause persistently inflated (>1.1) values of r-hat in a community occupancy analysis?

    Hi all, I'm trying to fit a couple of community occupancy models and am noticing that r-hat values for certain parameters are well above 1.1 (in the 1.3 - 1.6 range) even with fairly long runs (like, 200,000 iterations w/ 100,000 burn-in).  The model structure includes Bernoulli inclusion parameters associated with all beta parameters.  At any rate, the problematic r-hat values are consistently associated with the precision hyper-parameters for the betas.  Covariates with essentially no model support seem to converge slightly better (or at least have lower r-hats for the precision hyperparameter) than covariates with some support.   Strangely, these r-hat values also seem to stabilize pretty quickly (like, the difference between 15,000 iterations and 50,000 iterations is minimal). I'm curious to hear if anybody else has encountered this.  My kind of desperate explanations are

    1. The model just needs to be run out longer.
    2. I should increase the thinning rate (the trace-plots indicate that the tau chains will occasionally make pretty massive leaps that might be inconsequential if culled by thinning).
    3. This is related to the Bernoulli inclusion parameters turning the betas on and off, and r-hat wouldn't be expected to approach convergent values unless the inclusion probability were very close to 0 or 1.
    4. This is related to tau hyper-parameters themselves, which might not be expected to be distributed roughly normally.
    5.  The taus are derived nodes based upon stochastic sigma hyperparameters, and I should be tracing the latter instead.

    Sorry for the book.  Thanks for any help!

    Robert James McClelland · Liverpool John Moores University

    Interesting problem, I don't have an answer but have an example that may increase your understanding? My first thought was something's wrong, not to try and explain why it may be greater than 1. So I did some searching and found this example of where r-hat can yield unusual answer in a vector problem - hope it helps and doesn't make more complicated? I think there is something in there that might help?

    Let’s suppose, just to make this discussion more concrete, that rˆ is at 36.0° (counterclockwise from the +x direction in the x-y plane)

    The fact that a unit vector has a magnitude 1, with no units, means that if you multiply a unit vector by a scalar, the resulting vector has a magnitude equal to the value- with-units of the scalar. So for instance if you multiply a vector (r-hat) by 5.00 m/s, you get a

    Velocity vector 5.00(m/s)rˆ which has a magnitude of 5.00 m/s and points in the same direction as the unit vector rˆ . Thus, in the case at hand, 5.00(m/s)rˆ, means 5.00 m/s at 36.0°. The message here is mixing vectors and scalers (data) can yield anomalous results

  • Thijs Van der Vaart added an answer in Statins:
    What is the maximum dose of statins in children with hypercholesterolemia?

    Use of statins for treatment of familial homozygous hypercholesterolemia: What is the earliest age for initiating statin therapy and what is the maximum dose used in young children.

  • Hamid Rahmanei asked a question in Multiple Input:
    What's the differences between SISO and MIMO systems ?

    hi

     there is a question here, what is the differences between a SVFC design for a single input system and Multiple input one, in general ? i mean while founding coefficients k for u = -k x is there a big difference or what ? please open my mind in this question. thanks alot

  • How I can connect strategic management to firm performance in a measurable way ?

    strategic actions affect firm's financial performance

    Subhash C. Kundu · Guru Jambheshwar University of Science & Technology

    Prepare a scale on strategic orientation of the firm, strategic fit, various strategies like differentiation, cost leadership, focus strategy, etc by studying various research papers and also prepare a measure on financial performance and see the linkage. You may also find scales on strategic mgt and firm performance developed by others while studying various literature.

  • Fikrat Hassan added an answer in DNA Polymerase:
    How can I extract and purify cloned DNA polymerase?

    Is there any protocol to extract and purify cloned DNA polymerase from bacteria?

    Fikrat Hassan · University of Baghdad

    By isolation a gene that code DNA polymerase enzyme ( Taq DNA polymerase) from bacteria such as Thermus aquaticus . Then this gene is cloned in another bacteriaby using one of vector to form recombinant DNA.  Recombinant DNA is expresed in this bacteria to produce  DNA polymerase, then purification process done.

  • What are the Boundary conditions for a Vibrating Plate Composed of Two Materials?

    For a rectangular plate with one half made of material A and the other half made of material B, what would the boundary conditions be at the interface?

    Soroush Sadeghnejad · Amirkabir University of Technology

    By no slippery condition I mean both two different plates can not slide on each other. If you assume 3 DoFs for displacement and 3 DoFs for rotation, you should have a complementary condition in the attached edge.

    You are right, you can choose w(L/2-,y)=w(L/2+,y) for 0<y<H and dw/dx(L/2-,y)=dw/dx(L/2+,y) and If there is a heat conduction problem you can apply kL*dw/dx(L/2-,y)=kR*dw/dx(L/2+,y).

  • Roohi S Ahmad added an answer in Bone Grafting:
    How do I know which type of bone graft should be used during grafting ridge defect?

    During our practice we facing a lot of cases which need bone graft to restoring ridge defect. We have many types of bone graft available.

    How we can decide which type of bone graft should be used?

    Roohi S Ahmad · Putra University, Malaysia

    In Orthopaedics we decide depending on the biology of the defect. If the pathology is ischaemia, a vascularised graft or an Iliac crest graft is ideal. If not, various synthetic substitutes may be used.

  • Maryam Mirdamadi added an answer in Fish Diseases:
    Can anyone help with the use of copper sulfate in fish disease?

    FMC (FORMALDIHYDE, MACHITE GREEN ,METHALINE BLUE)

    FMCS (FORMALDEHYDE ,MALACHITE GREEN  , COPER SULPHATE ) The second equation is correct  or not ? so please informs 

    Maryam Mirdamadi · University of Tehran

    against piscinoodinium (particularly)

    saprolegniosis

    snail

    monogenes

    dosage:0.1-0.2gr/1000lit in hard water or 0.05-0.1 gr/1000lit in soft water.

  • Jodi F Evans added an answer in PAS:
    Can anyone send me a lab manual for special stains, CFV stain, Trichrome, Oil red O and PAS?

    Principle, procedure for conducting lab experiments for students.

    Jodi F Evans · Winthrop University Hospital

    http://stainsfile.info/StainsFile/jindex.html Here is a link to a very helpful website that provides all types of staining protocols as well as the theory behind them.

  • Mario Roberto Dal Poz added an answer in Healthcare:
    Is there any questionnaire that can be used to measure healthcare workers performance?

    I need a questionnaire that can be used to measure healthcare workers performance in general .

    Mario Roberto Dal Poz · Rio de Janeiro State University

    Dear colleague

    This is a very interesting and important HRH research and management topic. Here you have a few references:
    http://www.human-resources-health.com/content/10/1/41
    http://www.who.int/hrh/tools/situation_analysis/en/
    http://www.capacityplus.org/files/resources/HRH_Indicator_Compendium.pdf
    http://www.biomedcentral.com/1472-6963/13/355

    In addition, a few templates, if you can read in Portuguese:
    https://pt.surveymonkey.com/mp/hr-survey-templates/

    All the best

    Mario

  • Edward Barrall added an answer in Origin (software):
    How will I determine the baseline of DSC plot for calculation of area under the curve?

    I have a DSC plot of an alloy,for that i need to calculate the enthalpy change. How will I draw the baseline to calculate the area under the DSC curve say using origin software?

    I agree with Bedii Erdemir.  Alas, unsucessful runs do happen...  Well, that's science!  Being able to separate the good from the bad is called experience.  

  • Roohi S Ahmad added an answer in Bone:
    What is the diameter of vessels in the bone?

    What is the diameter of vessels in the bone?For example, tibia. Many thanks.

    Roohi S Ahmad · Putra University, Malaysia

    You mean the nutrient vessels?

  • How do we improve nurse-to-nurse communication when transferring patient unit to unit?

    I work on Inpatient Acute Rehab in a large urban hospital, and we do get telephone report from acute units when receiving/admitting a patient, but communication needs to be improved.  Suggestions to make that happen?

    Gwen R Rempel · Athabasca University

    I pediatric settings there is increased involvement of parents in the transfer communication process - parents are present during the in person transfer communication - pediatric intensive care unit to ward.

  • Jodi F Evans added an answer in H&E Staining:
    What is the optimum time required for rat brain fixation after trans-cardiac perfusion?

    For H&E staining and immunohistochemistry studies of brain tissue, we performed trans-cardiac perfusion with 4 % formaldehyde and then post-fixing in 4% formaldehdye for 24 hours. But I could not get good sectioning, tissue separated from paraffin. Is it related with perfusion time or anything else?

    Jodi F Evans · Winthrop University Hospital

    I agree.  It sounds like your porblem is with the embedding and not the fixation.  You may want to increase the time of paraffin infiltration.