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  • George Dishman added an answer in Semiconductor Electronics:
    Why do we use Ib instead Vbe as a parameter when measuring common-emitter output characteristics?

    As a rule, the BJT common-emitter output characteristics are presented as a function of the collector current IC of two variables - the collector-emitter voltage VCE and the base current IB; IC = f(VCE, IB). The base current serves as a parameter to obtain a family of characteristics.

    But we know (and discussed many times) that actually the collector current is controlled sooner by the base-emitter voltage than the base current. Then why not use the base-emitter voltage instead of the base current when measuring output characteristics of the bipolar transistor - IC = f(VCE, VBE)?

    Maybe we should use one or the other characteristic, depending on how we drive the transistor - by current or voltage. Or maybe it does not matter?

    This question is dual to the question about CB stage:


    George Dishman

    At the end of the day, the reason has been mentioned indirectly above. Of the electrons  flowing through the emitter, most go to the collector but a small proportion go to the base creating the base current. The fraction is well defined by the doping and geometry and base-emitter voltage is a secondary effect.

  • Yang Qiuju added an answer in Cluster Analysis:
    With the same feature extraction, why obtaining perfect classification but clustering into a class?

    I am doing clustering, but I am puzzled. The image dataset and two features (i.e., LBP and moment) were used for classification before, with which we obtained very good classification performance using k-NN classifier and the data were classified into 4 classes.

    However, when those data and features are used for clustering, we always get only one class! Specifically, with those methods automatically determining cluster number, like density-based clustering methods, they always acquire only one cluster; with those methods needing pre-defined cluster number, like spectral clustering or fuzzy clustering, when we per-defined 4 clusters, the clustering results are always that one cluster includes most of the data, and the other three clusters include very few data.

    Who knows how to solve this problem and what should I do?

    Yang Qiuju

    @Richard Hyde, thank you very much for your long answer.

    The data I used are auroral images. An aurora is a natural light display in the sky, predominantly seen in the high latitude (Arctic and Antarctic) regions.

    The morphology of aurora phenomenon changes gradually, which seems the images form a continuum.

    There are a lot of classification studies in the field of space physics, where the studies are done manually by using auroral morphology information. However, there is no unified classification mechanism, this is why I want to try clustering.

  • Uzzal Dash added an answer in Variogram:
    How can I estimate the major axis and ratio values from directional variogram for modeling anisotropy?

    I am new in kriging analysis. I am attaching a directional variogram produced by gstat package in R. Please take a look.

    I have plotted this directional variogram for PM10 data(particulate matter) in 4 direction to model the anisotropy. Data was in normal distribution.  I assumed Geometric anisotropy. In gstat, to model the anisotropy, I need the major axis (axis of major range) and ratio (minor axis to major axis).  

    what could be the value of major axis and ratio for this plot? In my sense, here 45 degree direction is major axis. Am I right? Then what should be the value of ratio?

    Most of time I am facing this kind of problem in eye estimation.Is there any easy and specific way to do this? Could anyone please enlighten me in details on this issue? I have read many documents upon this but I am not clear yet.

    Uzzal Dash

    Dear  Pedro Correia, Thanks for your detail answer. But probably for being a newbie, I couldn't understand some part. Whatever, I have a specific question.

    What I know about anisotropy modeling using gstat package is, after plotting the directional variogram, I need to find the major axis (the direction of maximum range) and the ratio (range of minor axis(orthogonal to major axis)/ range of major axis) by eye estimation. [because its complex to fit the separate model for every direction and determine the range]

    (My concept might be wrong)

    So, I have already attached my directional plot. now I have to tell gstat, the value of major axis and ratio. My question is, according to your opinion what could be the value of major range and ratio based on my attached plot?

    [the model you can see on my plot is just a general model which I fitted for isotropic variogram.you can ignore this model]

    [[I am attaching the 10 degree directional plot(as you said) and my R code using gstat package]]

    + 1 more attachment

  • Hamida Darwish added an answer in Surface Morphology:
    Is there any relationship between surface morphology and photoluminescence (PL) of al-doped ZnO film?

    Films which has rough morphology as well as island type morphology got broad spectrum in PL data but those films which are grown with columnar manner shows narrow spectrum?

    Hamida Darwish

    No there is no relation . but the broad PL spectrum  can comes from the doping  concentration or contamination. More concentration doped gives  more broad peaks or PL spectrum.

  • Anoop Kumar Srivastava added an answer in Soil Fertility:
    How can we proceed for decision on soil resource-based cropping sequence?

    Development of soil resource inventory of a given area , is considered highly imperative to take decisions on the options about the suitability of different crops in a farming system mode. At the same time, the information on edaphological requirements of different crops , is equally paramount , so that both are super-imposed in such a way, to delineate soil-crop analogues. This will pave the way for better land utilization efficiency. My further querries in this regard are as follows:

    * How should we develop a soil resource inventory ?. Shall we go for master soil pfofile stdies  or follow the grid- based soil sampling  coupled soil profiles to be later used for developing soil fertility variograms?. 

    * How shall we identify the soil fertility constraints of multiple nature from such soil resource inventory?.

    * What methodology , shall we adopt to identify   optimum soil requirement for different crops ?.

    * How should we identify the cropping sequence based on such soil resource inventory?.

    * Whether cropping sequence and land utilization efficiency are inter-related ?.If so , in what way?.

    I request my esteemed colleagues to share their experiences on these issues. Regards

    Anoop Kumar Srivastava

    Thanks Dr Nazir  for such an outright emotional response , but truly logical in  implementation and consequences. Yes  Dr Nazir , you  are dead right , we need to educate our  farming community to keep an vigilant eye on the annual changes in soil properties that undergo with every crop harvested from their field . An equally vigilant eye is also needed now with so much growing concerns about the environment , it could be even underground water quality . But Dr Nazir as a student  of soil , how do feel , is it not so alarming that there is least intervention of the soil-based information in shaping up the cropping sequence in a given farming system mode. Dr Rao  has rightly highlighted , farmers have their own choice of crops , irrespective of what your soil recommends.  And Dr Deka has really rejuvenated the whole discussion .

  • Cyril Mechkov added an answer in Electronics and Communication Engineering:
    Is virtual ground concept a property that arises due to the internal structure of opamps or due to circuit configuration
    Can virtual ground concept be used for opamps without negative feedback configurations
    Cyril Mechkov

    We have already made some humble attempts to explain the secret of CFA:


  • Gowhar Naikoo added an answer in Nanocrystals:
    How one can say that transition occurs from 4T1 state to 6A1 state in emission spectra of CdS nanocrystals?

    In emission spectra of CdS nanocrystals, transition occurs from 4T1 state to 6A1 state. 

    Gowhar Naikoo

    you can confirm it by doing ESR study  and UV/Visible Diffuse Reflectance Spectroscopy

  • Richard Gloaguen added an answer in Multispectral Imaging:
    Fabry-Perot Interferometer + CCD camera: novel multispectral imaging system?

    Has anyone used a Fabry-Perot Interferometer coupled with a digital camera to acquire a multispectral imaging system? 
    I found a multispectral system developed by VTT in Finland which uses a interferometer as a tunable optical filter, thus allowing for the construction of a CCD/CMOS based multi-spectral imaging system.
    Does anyone has experience with that? It seems very promising. 

  • Wang Tianyi asked a question in Motion Capture:
    How to use the motion capture for the research of fall experiment?

    1.Has anyone done this kind of research before?

    2.What shall I pay attention on the research?

  • Hamed Mahmoud soltani asked a question in Gaussian:
    Results at integration points?

    how can read stress results at Gaussian points?
    (for example in plane182 element)

  • Thomas Popp added an answer in SiO2:
    Etching of SiO2 in BHF?

    Is it OK to etch the wet oxidation deposited SiO2 in BHF solution? Will that have effects on the device performance? I am planning to fabricate FETs based on 2D layered materials (Mos2, WS2). The desired thickness of SiO2 was 300 nm, but the obtained thickness is about 330 nm. If anyone has done so, what could be the roughness difference in the as deposited and the etched SiO2? Please suggest me on this.

    Thomas Popp

    Hello, wet oxidation of a Silicon Substrate produces a a oxide of a good Quality. The selectivity of the BHF etching of SiO2 to Si is very high. If you etch away the whole oxide, the surface of the Silicon wouldn´t change at all. The etching in the oxide is isotropic. That wouldn´t be the case, if you would use a stack of a second oxide, for example a CVD oxide made of TEOS. But as you have that high Quality oxide, you should not introduce much roughness.

  • Stefan E Matthiasson added an answer in Vascular Surgery:
    Vascular surgery: What is the energy needed to obliterate a great saphenous vein using EVLT 1470nm? In total J ? and J/cm
    And the energy needed using 980nm laser ?
    Stefan E Matthiasson

    We use the radial fiber and for the last two years the double ring radial fiber. Honestly, I am not sure if that’s necessary. However, our standard use is 70 J/cm. My “gut feeling” is that lower energy is not enough. No scientific grounds for this statement, I have to admit. But it works fine.

  • M. H. Hashempur added an answer in Systematic Reviews:
    How can I define quality in systematic review and meta analysis?

    Can someone suggest me what is the best tool to use in a systematic review to determine the quality of each clinical trial included in the review itself? I'd like to use a tool that provide a quality score for each included paper. Thanks!

    M. H. Hashempur

    Dear Irene

    there are 2 suggestions. One of them is PRISMA check list which enable you to evaluate systematic reviews by an objective manner. The checklist is accessible via this link: http://www.prisma-statement.org/2.1.2%20-%20PRISMA%202009%20Checklist.pdf

    Another suggestion is using Cochrane scoring style. you can see this style on Cochrane  website.

  • Snehaa Chandrakumar added an answer in Epithelial-Mesenchymal Transition:
    Do metastatic lines reqiure MET (mesenchymal to epithelial transition) when inject intravenously in for colonisation?

    we know that  EMT  is critical step for metastasis  ,then these metastatic cell require MET in establishment and stabilization of distant metastases. but what about cell lines taken from metastatic site , will they undergo EMT when inject intravenously and thus require MET in order to colonize metastatic site.?

    Snehaa Chandrakumar

    Obviously metastatic cells require MET after EMT for colonization.

  • Sayan Dey asked a question in IDE:
    How can I increase the response and reduce the recovery time of a sensor prepared by nickel oxide nanostructures?

    I am preparing gas sensors with NiO coral like nano structures (in the form of thin films/drop casted on IDE). I am getting good sensitivity for NO gas but the response is poor (around 41%) and the recovery time is also poor. The recovery rate is very slow. Please suggest me the possible modifications that I can do to improve the response and reduce the recovery time of the sensor. Please suggest me if doping is required to reduce the bandgap (3.4 eV for NiO) or formation of some p-n junctions is necessary. Please suggest the synthesis steps for the same.

  • Syed Muzamil Ahmed asked a question in Zinc:
    How zinc and tourmaline as a catalyst change the morphology of CaCO3 form Calcite to Aragonite ?

    i read zinc and tourmaline as a catalyst at a constant pressure and temperature change the deposited CaCO3 morphology from Calcite to Aragonite on hot surface. i need the Mechanism and reaction involve in the process.


  • Gowhar Naikoo added an answer in Carbon:
    Is pentavelency of carbon possible in case of intermediates found in IRC calculations?

    I have a reaction in which an intermediate is having a negative charge on oxygen. when i located the TS and i did IRC i got an intermediate in which the oxygen which should have negative charge has formed double bond with adjacent carbon and that carbon shows pentavalency,,,is it possible in case of intermediates.

    Gowhar Naikoo

    pentavalency of carbon is generally deadly impossible. 

    Using X-Ray to Investigate the Possibility of a Pentavalent Carbon Intermediate, Preliminary X-ray analysis of molecules that have been designed to favor a carbon with five bonds seemed to suggest the possibility of a pentavalent intermediate in SN2 reactions .

    I hope you will understand me

  • Santi Lata Sahoo added an answer in Phytochemicals:
    How do I get lingands for my plant of interest. Am new at molecular dockings, is there a database that tells all the phytochemical in a plants?

    am interested in molecular dockings for anti diabetes plants

    Santi Lata Sahoo

    Most probably according to the habitat the phyto-chemical constituent of the plant varies.So you enter to the collection site of the plant and to the data base of phyto-chemical constituents of anti diabetic plant. Hopefully this will solve your problem to some extent because plants also exhibit systemic variation and seasonal variation.

  • Amandeep Kaur asked a question in Urbanism:
    What is the difference in Unauthorized Colonies and non-notified Slums?

     Particularly in Urban areas

  • Thomas W Stief added an answer in Blood:
    What are the blood biochmical parameters which are hampered by haemolysis of blood?

    what are the blood biochemical parameters which are hampered if it is estimated from the serum of haemolysed blood? does it alter the results while estimating hormones in these samples?

    if any references and literature please suggest?

    Thomas W Stief

    Free hemoglobin will increase to > 0.1 g/l, NSE will increase by about 4 µg/l per 0.1 g/l free hemoglobin. LDH-1 and ASAT (= GOT) will increase.

  • Tej Pratap asked a question in Friction:
    How to use user defined formulation in abaqus?

    in place of predefined frictional contact i want to use user defined frictional function and its value.

  • Zahra Akramzadeh asked a question in Eyes:
    Reading feelings from eyes.

        There are lots of films that shows someone can easily say what you are thinking of or what is your feeling about something just by looking in your eyes and it is not too far to believe for us.it is known that thoughts can be shown from different part of body, but is there experiments that prove one’s thoughts are related to his\her eyes?

  • Adrian Vaduva asked a question in Gross Pathology:
    Does anybody know a manufacturer/reseller for large glass containers for organ storage - pathology museum?

    We need to replace some of the broken glassware and bring in new specimens for the pathology museum and we are looking for proper glass jars or equivalent to display gross pathological specimens.

  • Konrad Neumann added an answer in Method Validation:
    Method development for determine VOC using HSGCMS?

    I been running a method validation using Head space GCMS, but encounter some problem, now is there is high saturation of chromatogram at the start? what else can I improve and have a proper peak?

    Other comment also appreaciate.

    Attached with all the setting and chromatogram

    Konrad Neumann

    Hi Liang!

    Did you define Start and end time properly? And did you use the correct tunig file? You can Set the detector voltage to 1 or 1.2 Kv manually and test if SIM works. It Sounds very strange to me.

    Maybe I used a Rxi ms. But 2.5 min difference is very much at the beginning of the chromatography.

    I used likens-nickerson distillation and did a normal liquid injection for analysis of paintings. But this is very time consuming. 

    Your method could work. But i would test stability of the analytes at that temp.

    Best regards, Konrad.

  • Federico Y. Fontana added an answer in Regression Analysis:
    Can anyone explain be briefly what is the significance of F-test in Regression analysis

    I have been trying to establish relation between dependent and independent variable for that i have used regression analysis and checked its relation using R2 value. But i also want to validate with F-test.

    Federico Y. Fontana

    Hi Bhargav, 

    Usually F is the amount of systematic variance divided by the amount of unsystematic variance in the model fitted; put simply, the F-statistic is the ratio of how good the model is compared to how bad it is (a good model should have a large F-ratio).

    In GLM its significance level tells you the probability of getting an F at least this big if there wasn't an effect in the population. This value is obtained compared your value of F against the maximum value we would expect to get by chance if the group means were equal in an F-distribution with the same degrees of freedom; if the value we obtain exceeeds this critical value we can be confident that this reflects an effect of our independent variable (both in using regression for groups mean comparison or to 'establish' a linear relationship between variables).

    Again, put simply it tells you (if its significant) that the model you fitted to the data is better than a flat model indicating how much your model has improved the predecition of the outcome compared to the level of inaccuracy of the model. 

  • Danelyn Tamis Delos Reyes asked a question in Gymnosperms:
    Can anyone give me an example of angiosperm species that has the characteristics of a gymnosperm? Or vice versa?

    Like for example,Casuarina equisitifolia.

  • Tofigh Saadi added an answer in Change Detection:
    Can I study extreme precipitation changes detection and attribution to climate change for basin scale without downscaling the CMIP5?

    Also can I use the SDSM for downscaling the Control run and historical forcings of CMIP5 for study detection and attribution?  

    Tofigh Saadi

    Hi Mr Singh,

    Thank you for your answer.

  • Mahmoud A Hammad added an answer in Hydropower:
    While working on a new Hydropower project. Having flows&topo is there a deterministic/statitic method to the select the best design flow?

    While working on a new Hydropower project. Having flows&topo is there a deterministic/statitic method to the select the best design flow?

    Mahmoud A Hammad

    Facing this problem for micro hydro power systems as seasonal flows require that comparison be carried out on yearly accumulated power out puts.

  • Shrish Shukla added an answer in OpenFOAM:
    How can I implement an efficient 3D mesh topology for CFD simulation of turbine blade

    I´m developing a tool to generate an openFoam wind tunnel case. I already have the blade geometry constructed, but I'm really new to CFD and parametric meshing. I found some articles where they mention the existence of  O,C,H and I topologies to mesh the airfoil and also some software (bladedesigner) that use a topology named O10H, but none of these has a reference about how to implement the geometry of these topologies and if there are others. They also do not specify what the best use cases for each one.

    Can someone help me to get started making an efficient mesh for my tool?

    in the attached file show an example of the different s mesh topologies that I found, and also my example blade

    + 5 more attachments

    Shrish Shukla

    Go for Turbogrid it is particularly design for creating automatic hexa mesh around blades profile. Besides, you can also follow ICEM for meshing but you wont able to create automatic blade passage in ICEM.

  • Pepijn de Vries added an answer in R:
    Any advice in flowchart in R presentation?

    Hi friends,

    I am working in a reproducible presentation in R where I've to show some numbers in the form of a flow chart. I tried some packages like DiagrammeR but they give error messages when I put in the R chunk.

    Is there any other way?

    Pepijn de Vries

    I've used the diagram package (https://cran.r-project.org/web/packages/diagram/) in the past with success. Without knowing what your exact problem is, I suggest you have a look at this package...