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  • Piotr Cizkowicz added an answer in Time:
    Time Trends Vs Time Dummies?

    Can I include both time trends and time dummies when running panel data? What is the difference between them? I think that my data may have problem of unit root.

    Piotr Cizkowicz · Warsaw School of Economics

    Time dummy is a variable which equals 1 for a given year and 0 for all other years. It allows to control for time-specific fixed effects i.e. shocks which impact is restricted to a given time-period, affects or panel units and are not controlled by other explanatory variables. Normally you should  include T-1 time dummies (for T being time dimension of a dataset) but it can be restricted if you have some strong prior as to where the time-fixed effects should occure (e.g. war years). Time trend is a variable which is equal to the time index in a given year (if your sample includes years 2000-2010 than time trend variable equals 1 for 2000, 2 for 2001 etc.). It allows to control for the exogenous increase in the dependent variable which is not explained by other variables. You may include both type of variables simultaneously as long as you have some solid explanation, however neither time-dummies nor time trend is a solution to nonstationarity (unit root) issue. I would recommend that you first check stationarity of your data with the use of panel unit root tests.

  • Dorian Aur added an answer in Cognitive Systems:
    Is Chalmers' so-called "hard problem" in consciousness real?

    In his 2014 book "Consciousness and the Brain: Deciphering How the Brain Codes Our Thoughts" Stanislas Dehaene wrote "Chalmers, a philosopher of the University of Arizona, is famous for introducing a distinction between the easy and the hard problems. The easy problem of consciousness, he argues, consists in explaining the many functions of the brain: how do we recognize a face, a word, or a landscape? How do we extract information form the senses and use it to guide our behavior? How do we generate sentences to describe what we feel?

    “Although all these questions are associated with consciousness,” Chalmers argues, “they all concern the objective mechanisms of the cognitive system, and consequently, we have every reason to expect that continued work in cognitive psychology and neuroscience will answer them. By contrast the hard problem is the “question of how physical processes in the brain give rise to subjective experience … the way things feel for the subject. When we see for example, we experience visual sensations, such as that of vivid blue. Or think of the ineffable sound of a distant oboe, the agony of an intense pain, the sparkle of happiness or the meditative quality of a moment lost in thought … It is these phenomena that poses the real mystery of the mind”."

    Stanislas Dehaene's opinion is "that Chalmers swapped the labels: it is the “easy” problem that is hard, while the “hard” problem just seems hard because it engages ill-defined intuitions. Once our intuition is educated by cognitive neuroscience and computer simulations, Chalmers’ “hard problem” will evaporate".

    Personally, I agree with Stanislas Dehaene's opinion.

    Dorian Aur · Stanford University

    Dear Marc,

    What is your candid opinion about physics?

  • K.Kamil Reza asked a question in Long non-coding RNA:
    Why long non-coding RNAs are important for cancer diagnostic

    I would like to know about the non-coding RNAs as cancer biomarkers

  • How could I choose a good subject for my thesis?

    I want to choose some good subject for my phd thesis.Can I use game theory to analyze international economics?If I can, in what fields?

    thank you

    Hussein Elasrag · Ministry Of Industry And Foreign Trade

    Thinking about the end result, your examiners will be looking for research which is;

    novel (original)
    set in the context of the existing research in the field, and
    competently executed
    When choosing a thesis topic, it makes sense to use these criteria to help you.




  • Dr Murugesan Muthu added an answer in Composites:
    What are the thermal tests that can be done on Polymer Matrix Composites?


    Attached is a picture of an aircraft graded carbon/epoxy composite. Out of curiosity, what are the possible thermal tests and hence properties that can be investigated from such sample?

    Any contributions will be valued.

    Thank you.


    Dr Murugesan Muthu · Imperial College London

    Mechanical properties 


    Surface roughness


  • Maria Alexou added an answer in Hydroxyl Radical:
    Can hydrogen peroxide scavenge hydroxyl radicals?

    please provide proper information...

    Hello. H2O2 gives OH in the Fenton reaction. OH is so reactive, that it can react with anything prior to the molecule it came from, having such a short lifetime compared to H2O2. There are really a lot of compounds that can react with OH "easier" than H2O2 would. (See also "ROS-mediated redox signaling during cell differentiation in plants" by Romy Schmidt and Jos H.M. Schippers). Best regards.

  • Mohamed El Tabbal asked a question in Imaging:
    Does anyone know a company that provides coverslips in range of 1.5-2 mm diameter used in imaging ?

    I use the cover slips to  place it over chronic surgical brain window

  • Are there examples of macromolecular surface diffusion on mica ?

    I'm looking for (macro)molecules that are known to exhibit lateral diffusion on mica in aqueous solutions. Ideally, they would have a high affinity for mica (to limit the required concentration in the liquid bulk) and they don't self-associate into 2D clusters. So basically I'm looking for a molecular 2D "gas" that forms spontaneously without having to change the surface chemistry of mica. Any ideas ?

    Louise Deschênes · Food Research and Development Centre

    The following papers may be of some interest to you:
    Kumaki et al., Peculiar ‘Reptational’ Movements of Single Synthetic Polymer Chains on Substrate Observed by AFM. Macromol. Rapid Commun. 2008, 29, 406–411.
    Roiter an Minko, J. Phys. Chem. B 2007, 111, 8597-8604.

  • Sudev Naduvath added an answer in Graphs:
    Can anyone give list of operations of digraph/directed graphs ?

    Frequently i search digraph operations in internet.but i cannot get any article and book. 

    can anyone give list of operations of digraph/directed graphs ?

    Sudev Naduvath · Vidya Academy of Science & Technology

    Please refer the following material.

    J. B. Jensen and G. Gutin,  Digraphs Theory, Algorithms and Applications, Springer Verlag, 2007

  • Would you kindly join me in wishing a happy birthday, and pay homage to our dear RG friend LJUBOMIR JACIC?

    i just remembered that our dear friend Ljubomir was born on the 28th of March, a few years ago.

    I pay tribute to an inteligent, sensitive and sensible sweet adorable Serbian.

    You, dear sir, are a very special person, that I feel honoured to have met, and  thank you for letting me be your unconditional admirer !

    (I do hope that Î got the date right.... If not, please consider this a singular extravagant note of friendship, )

    Yours, truly, with warm respects !


    Rajshree Dayanand Katke · Grant Medical College

    Happy birthday to you sir

  • Rizk Sarhan added an answer in Joining:
    Can we make online case discussion group or is there any site provide case discussion other than commentaries?

    i hope to join online case discussion 

    Rizk Sarhan · Benha University

     start by my self

    female patient 53Y  uncontrolled DM   20Y ago  c/o of dyspnea and generalized fatigue 7 d ago  NO fever no other symptoms investigation till now

    CBC: HBG  10.7  NN  WBC 10   N:5   LYM: 3.5   PLT :466

    CRP:12      ESR: 1ST 85   2nd    148    

    urea   56mg/dl     urine  A/C ratio   0.16

    uric acid   5   albumin   3.53

    Chest x-ray: bilateral minimal pleural effusion

    abd u/s: enlarged RT liver lobe 22.5cm midclavicular line (fatty liver), muddy gall blader, minimal ascites, no other abnormalities 

    echo: hypertensive heart disease wih LV diastolic dysfunction and degenerative MV  and AV  EF:65%

    which next :

    1- pleural effusion sampling with u/s or ct guided and analysis esp. for adenosine deaminase (TB)

    2- search for collagen disease :  SLE

    3- abd and chest  CT with contrast

  • What statistical test would be used for this occurrence setup if possible?

    Suppose I had 4 treatments done to mice to determine when normal bowel movement would occur faster or as near to treatment (a).
    a) no treatment, negative control
    b) antibiotics only
    c) antibiotics with probiotic A
    d) antibiotics with probiotic B
    The setup goes this way: I did an estimation of population mean to find a range, based on the (a) group, where my mean rate of droppings could be, and used that to determine whether a mice pooped within that range. The test will be a yes-no test. But what then? The number of mice that could normalize bowel movement would increase overtime and it may take long so I may have to cut short the experiment and make do with my temporal data, but (Q# 1) how do I go about analyzing said data. Sorry for the long explanation. But furthermore, taking into account that there is the (b) group which is antibiotic only, what would happen if this group normalizes bowel movement earlier than the with-probiotics groups (Q#2) will there still be further statistical analysis to be done or will that just automatically result to failure on the part of the assumption that the two probiotics had benficial effects on the mice bowel movement.

  • What is Optical and Photonic band gap?

    What is the major difference between optical band gap and photonic band gap?

    Optical band gap has the same units as that of energy band gap while photonic band gap is the range of forbidden frequencies in a material. How is the optical band gap related to energy band gap and in what way does it differ from photonic band gap?

    Anurag Tyagi · University of California, Santa Barbara

    I'd just like to add that optical bandgap (more accurately "electronic bandgap") and photonic bandgaps are electron/photon analogs. Electronic bandgap arises from a periodic crystal lattice (atomic spacing is on the same order of magnitude as electron bloch wavefunctions). Likewise photonic bandgap arises from a "photonic lattice" (as explained above) with feature dimensions of the same order as the photon wavelength. This analogy is reflected in the mathematical calculations for deriving the bandgaps. The differences arise (of course) because electrons/photons are Fermions/Bosons respectively. 

  • Daniel Becker added an answer in Epidemiology:


    Daniel Becker · University of Georgia

    I agree with Manuella, these are very simple concepts that could be gleamed from quick reference to any introductory epidemiological textbook or search on Google.

  • Luis Felipe Ateca Torres asked a question in Universe:
    What could happen if our universe continues to expand?

    If there are multiple universes and our universe is expanding. This indicates that our universe could collide and / or merge with another universe.

  • Iqbal M N asked a question in Antibodies:
    Anyone please share how to use antibodies for therapy?

    Anyone please share how to use antibodies for therapy? I want to develop antibodies and then use for therapy.

  • How far has Kissinger's "World Order' helped to 'understand' the 'structural changes in global system with emergence of new pillars and power hub?

    World Order' by Kissinger

    Patrick M. Morgan · University of California, Irvine

    The Kissinger book is an excellent effort to explain the evolution of order and management in the international system over a long period and a good guide to thinking about how to pursue world order and global security management today.  Since the existing arrangements to manage global security that emerged after the end of the Cold War are now under considerable strain, this is a good subject to explore these days. 

  • Jane Lindborg asked a question in Annexins:
    Does anyone have a protocol for the in vivo injection of annexin v in mice to potentially block phagocytosis?

    I'm also looking for a company that sells annexin v for this purpose.

  • Louis Brassard added an answer in Chimpanzee:
    Have primate species other than Homo sapiens engaged in acts of aesthetic creation?

    For several years some scholars have accepted the engraved pieces of ochre from Blombos cave in South Africa, at least one of which has a geometric cross-hatched pattern, as evidence of early modern human aesthetic creation (ca. 75,000 BC). See: Henshilwood, Christopher S.; d’Errico, Francesco; et al., “Emergence of modern human behavior: Middle Stone Age engravings from South Africa,” in Science, new series, vol. 295, no. 5558, February 15, 2002, pp. 1278-1280 (http://www.sciencemag.org/content/295/5558/1278.abstract?sid=da7c3755-b2bc-4ced-93da-2c024c50b1fd, access: March 14, 2015).

    The recent discovery of similar engravings on shells on Java, from ca. 500,000 BC -that is, long before the emergence of modern Homo sapiens-, suggests that aesthetic creation evolved gradually. See: Joordans, Josephine C. A.; d’Errico, Francesco; et al., “Homo erectus at Trinil on Java used shells for tool production and engraving,” in Nature, December 3, 2014 (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13962.html, access: March 14, 2015).

    Suggestions that chimpanzees make aesthetic decisions while painting are intriguing. See the following texts and video:





    Can anybody point me toward additional studies on aesthetic creation by nonhuman primates, either in the archaeological record or among our contemporary primate cousins?

    Forms in nature, not only in biological forms but in all forms studied by physics, chemistry, archeology, architectures, etc. etc. are created by symmetry breaking events in process of generation of forms from surfaces.  Any analysis of forms in any science including the process of vision or touch or hearing is thus a process of analysis of the generation of the form:  Structural hiearchy IS HISTORY.  All sciences indepently cames to this evolutionary outlook based on formal analysis of the forms under consideration.  All forms are a fossil of the symmetry breaking events of its generation.  General relativity is totally based on symmetry viewpoint.  Quantum mechanics is totally based on the symmetry formalisation.  Neother theorems express the most fundamental laws of conservations in physics in terms of symmetry.  The conservation of energy being the symmetry of the laws of physics relative to time.  If you diffuse an image or a topographic surface you gradually remove in an optimal mathematical way the symmetry breaking points/events of its formation (in a formal mathematical sense) in the reverse of its formal creation.  Look at any object and imagine its diffusion and you will see it disapearing in the reverse sequence of its formation. 

  • How to go for extraction of essential oils from Clerodendron inerme leaves?

    Friends, I am willing to try to extract the essential oil ingredient present in the leaves of Clerodendron inerme......the popular hedge plant....in tropics and topiary......i have tried hydrodistillation and ethanol based extraction but finding it difficult to seperate it from the solvent used.......

    B.R. Rajeswara Rao · Central Institute of Medicinal and Aromatic Plants

    Dear Surendra Nath

    I am attaching 2 publications on essential oils of Clerodendron species and 1 review article.

    I am also providing a link associated with the methods of extraction of essential oils.

  • Fulgencio Lisón added an answer in Bats:
    Is there a relationship between insects and bats activity in deciduous forest along leaf growth?

    The deciduous forest is a important habitat for insectivorous bats, they prey activity are depending by the availability of preys and consequently the abundance of insects is dependent on the vegetative state forests (growth state). Does anyone know of some good papers about this subject?

    Fulgencio Lisón · University of Murcia

    You are welcome. 

    But, do not forget the role of waterbodies ;). 

    There are many papers which showed that the presence of waterbodies were a keystone in the bat activity. Probably, these waterbodies are important areas for insect. 

  • Jan Antfolk added an answer in Meta-Analysis:
    Any good tools for Meta analysis except Biomercator?


    I am working on meta-analysis for QTLs and I need a good tool except Biomercator for nice and beautiful figures because Biomercator doesn't give beautiful and well effective figures. Can anyone please suggest me any tool that can give me beautiful figures for Meta-analysis? I would be highly obliged for your suggestions 


    Anuj Kumar
    Monsanto's Beachell-Baurlog International research scholar 
    University of Arkasnas

    Jan Antfolk · Åbo Akademi University

    I also recommend Excel or R. Making figures in R takes some getting used to, but the flexibility is good. 

  • Simone Orcioni added an answer in Crime:
    Is there a bigger crime in mathematics than "divide by 0"?

    We know that not checking the value of the divisor for 0 leads to such 'absurdum' as the following 'proof':

    Let us have x=0 hence giving a true equation x=2*x which we can simplify dividing both side over x getting: 1=2 which I belie is not true :) since we overlooked to give up the division operations since the divisor (x) was assumed to be 0.

    However, the "0 division" is a kind of definite (hence "death") phenomena.  Even a very very small divisor: 0.0000000000000000000000000000000000000000001 still can be used. So, my question is if you know any other "no case" which is similar to it but evidently different in nature (no division is involved :)

    [Pls hit the green ^ if you like it]

    Simone Orcioni · Università Politecnica delle Marche

    I agree with Daniel Page, hower not only in math but generally speaking in science, "cloaked arguments" are a plague.

    Doug Zongker's showed well, in his famous paper/presentation. Please follow the below link and have a fun.

  • Is mathematics a science? Is philosophy a science? What is science?

    Some people say both mathematics and philosophy are not science, because they deal with purely abstract entities. Still some others say both mathematics and philosophy are science, because the purely abstract entities they deal with are from objective world.

    From the ontology and form: Is mathematics a science? Is philosophy a science? What is science?

    Sudev Naduvath · Vidya Academy of Science & Technology

    Let me first quote the words of Richard Feymann "Nature speaks to us in Mathematics".

    Definitely Mathematics is science in the sense that it is a systematic, formulated, logical, and verifiable knowledge. In fact, Mathematics provides language (or mathematics is the language) for all sciences to explain, analyse and verify the findings.  That is why Mathematics is called the queen of all sciences.

    For me, Philosophy is not science, but every science has its own philosophy and  the connections of philosophy with sciences are deep and influential.

  • Luis Felipe Ateca Torres asked a question in Universe:
    What is beyond of our Universe?

    To expand a gas, room must be available. So if our universe is expanding. What is the space provided allows. Does this mean that our Universe is in an infinite room?

  • Emotional neglect is a psychogenesis of BPD?

    People with borderline personality disorder suffer from problems to regulate emotions and thoughts, have unstable relationships with others etc.

    My question is: is it possible that a person who has a self-destructive behavior, such as substance abuse, have a depression of any range due to an emotional abandonment?

    Jan Antfolk · Åbo Akademi University

    Emotional neglect have an effect (not very strong) on psychiatric problems later in life. The effect is not specific to BPD . Emotional neglect also seem to interact with the genotype of an individual so that some (but not others) are are at increased risk at developing psychiatric disorders. It is quite important to remember that most individuals who have suffered emotional neglect develop no psychiatric symptoms. 

  • Susette Mueller added an answer in MCF10A Cells:
    How can I achieve 100% penetration of my antibody in IF on 3D mammary structures?

    Hi all,

    I am growing MCF10A cells on Matrigel, so that they form 3D acini, fixing them after 16 days. Unfortunately, I have Ab penetration issues. I have tried 2-hour incubation in primary Ab, o/n at 4*C, o/n at 4*C with 0.1% triton and still face problems: the outer cells stain very well, whereas the central ones appear negative, while they should be positive for the stain. I have tried fixation in formalin and formalin+0.1% glutaraldehyde.
    I am sure it's a penetration issue. Anyone doing similar experiments/facing the same problems and any suggestions on how to overcome this???

    Thanks so much! Grateful for your answers!!!


    Susette Mueller · Georgetown University

    1.  By the way the glutaraldehyde was a bad idea because it will extensively crosslink and further block antibody access.  

    2.  The Trition is a very good idea, but you can also fix in the presence of 0.1 or 0.2% Tx with your formaledhyde to speed penetration and then post extractd with 0.5% triton to further increase antibody penetration.  Here is a link to a paper that not only is good for penetration but also to block the background which is notoriously high in matrix containing 3D structures.

    Curr Protoc Cell Biol. 2010 Sep;Chapter 10:Unit 10.18.1-20. doi: 10.1002/0471143030.cb1018s48.
    Imaging cells in three-dimensional collagen matrix.
    Artym VV1, Matsumoto K.
    Author information
    The use of in vitro three-dimensional (3-D) collagen matrices to mimic an in vivo cellular environment has become increasingly popular and is broadening our understanding of cellular processes and cell-ECM interactions. To study cells in in vitro 3-D collagen matrices, both cellular proteins and the collagen matrix must be visualized. In this unit, the authors describe the protocol and provide troubleshooting for immunolabeling of cells in 3-D collagen gels to localize and visualize cellular proteins with high-resolution fluorescence confocal microscopy. The authors then describe confocal reflection microscopy as a technique for direct imaging of 3-D fibrillar collagen matrices by discussing the advantages and disadvantages of the technique. They also provide instrument settings required for simultaneous imaging of cellular proteins with fluorescence confocal imaging and 3-D collagen fibrils with confocal reflection microscopy. Additionally, the authors provide protocols for a "cell sandwiching" technique to prepare cell cultures in 3-D collagen matrices required for high-resolution confocal imaging.
    © 2010 by John Wiley & Sons, Inc.
    PMID: 20853341 [PubMed - indexed for MEDLINE] PMCID: PMC2988473 Free PMC 

    3. The Johnson and Mueller paper attached outlines how to image collagen and autofluorescence without using any antibodies, although that may not satisfy your purposes.

  • How soon can the demyelinating process start in mild traumatic brain injury?

    Traumatic brain injury, even in its mildest form, is known to result in degenerative processes including demyelination and dysmyelination of the axons over time. The shearing and tearing of the axons (primary injury) due to the acceleration and deceleration force of high velocity impact would also normally trigger off the secondary injury cascades. This includes the synaptic deregulation, cell death and axonal degeneration.  

    But how quickly does these processes start (especially the demyelination of the axons) in patients with mild TBI? I am of the opinion that it will take at least a few days or weeks before such degenerative process starts. What are your thoughts?

    Chandramouli Balasubramanian · National Health Service

    I am not sure if injury to myelin is same as eating up of myelin by immune cells that have gone "mad" against their own body proteins! because traditionally de-myelination is used for a systemic (blood borne) process and not a central or peripheral nervous SYSTEM  process (mTBI) !

  • How can we bring together cross section and time series variables in the multiple linear regression model?

    for instance bank data which can be represented in panel and macroeconomic data which is time series?

    Piotr Cizkowicz · Warsaw School of Economics

    You can use both types of data in one panel data model. I don't know what exactly is your research plan but I assume that you are estimating a model in which the dependent variable is a bank-specific indicator observed in a given year and explanatory variables are either other bank characteristics or macroeconomic indicators. In this case your model may be of the form

    bank_ind1it=alfai+beta1*bank_ind2it+ beta2*macro_indt+epsilonit

    There are of course some issues while using specification of this type (for example you should use time-series unit root test for macro_ind and panel unit root tests for remaining variables) but they don't prevent from using this specification. I estimate this type of model in the attached paper (published also in Applied Economics).