Q&A

ResearchGate Q&A lets scientists and researchers exchange questions and answers relating to their research expertise, including areas such as techniques and methodologies.

Browse by research topic to find out what others in your field are discussing.

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Which part of solar spectrum is more useful in PV technology?

Photo voltaic system  gives better performance for which light UV, VIS, IR.

Chris Gueymard · Solar Consulting Services

The air mass, m, I talk about is just the photon pathlength relative to a zenith sun. So m=1 for a zenith sun and m=2 for a sun altitude of 30°. The rating of solar cells considers m=1.5. This is not directly related to the altitude of the tropopause.

What is the best non conducting material for transmitting ultrasonic vibration?

I want a material for transmitting ultrasonic vibration but it must be non conducting. Materials such as polymers are not good candidate because they don't good thermal resistance.

Salvatore Pullano · Universita' degli Studi "Magna Græcia" di Catanzaro

What is the transmission medium?

What is this diatom?

I have a classification problem with one species of diatom (see image). I found this diatom in fresh and clean water of Northern Italy.

It is a mono raphid diatom, probably Achnanthidium, length 38-42mm, width 6-8mm (10mm bar).

It does not seem to be present on the "Süßwasserflora von Mitteleuropa" of Kramer, Langhe-Bertalot and on "Diatomeen im Süßwasser Benthos von Mittleuropa".

Is there some expert who is able to recognize this species? Thanks to everyone!

Stefano.

Lawrence Vitug · De La Salle University

I think it achnanthes definetly you can check at western diatoms

• Can we find anti neuronal antibodies ( as Yo) in autoimmune diseases?

Is anti neuronal antibodies is exclusively found in cancers?

Sharad Purohit · Georgia Regents University

some patients with SLE and other autoimmune diseases do show antibodies to neuronal proteins.

• How do I perform a mediation analysis using pretest and post-test scores?

I have a between-subjects manipulation that has 2 levels (X). I want to see if this manipulation affects a performance score, Y. I also want to see a variable, which is measured before Y, would mediate the X on Y effect. So this is the classic mediation problem: X --> M --> Y

I measured both M and Y before and after the manipulation, so that I have M1, M2, and Y1, Y2. My research makes more sense in whether the change in M (i.e. M2-M1) explains the change in Y (i.e. Y2-Y1). A friend suggested me to do the mediation with the difference scores:

X --> (M2-M1) --> (Y2-Y1)

I'm also considering controlling the M1 score and Y1 score in building the mediation model, which should work like an ANCOVA when M1 and Y1 don't interact with X in influencing Y2.

Appreciate your help if you could let me know which way is a better approach in this question.

PS Also considered multilevel and SEM approach, but not quite feasible with my small sample size. That's why I wanna stick with the regression approach.

David MacKinnon · Arizona State University

Hello Henry,

See Chapter 8 in MacKinnnon (2008, Introduction to Statistical Mediation Analysis) for options with two waves of data and also options for more than two waves of data. There are several options with the pretest-posttest design including difference score, residualized change score, and analysis of covariance. Residualized change and ANCOVA general give very similar results except if there are substantial pre-test differences. The choice depends on the pattern of change over time that you would expect in each group if no intervention was delivered. If the groups were randomized, differences between groups are likely due to random error so regression to the mean would be expected over time--so ANCOVA and residualized change would be reasonable. If the groups are not randomized, a difference score method may be more appropriate as it allows for pretest differences to maintain over time. The ANCOVA model is the most general and it can be estimated with regression or SEM. The SEM approach is more general as it can allow for more complicated models such as models with latent variables and extensions to more waves of data. These issues are described in MacKinnon (2008) as mentioned above. The two wave ANCOVA model and multi-wave longitudinal mediation models are described in MacKinnon (1994: NIDA monograph) and applied to the mediation analysis of a steroid prevention program in MacKinnon et al. (1991; Prevention Science). I believe that both of these papers are on Research Gate. If you can’t get them on Research Gate, please contact me and I will send them to you.
Regards,
Dave MacKinnon

MacKinnon, D. P. (1994). Analysis of mediating variables in prevention and intervention research. In A. Cazares & L. A. Beatty (Eds.), Scientific methods for prevention/intervention research (NIDA Research Monograph Series 139, DHHS Pub 94-3631, pp. 127-153). Washington, DC: U. S. Department of Health and Human Services.
MacKinnon, D. P. (2008). Introduction to statistical mediation analysis. Mahwah, NJ: Erlbaum.
MacKinnon, D. P., Goldberg, L., Clarke, G. N., Elliot, D. L., Cheong, J., Lapin, A., et al. (2001). Mediating mechanisms in a program to reduce intentions to use anabolic steroids and improve exercise self-efficacy and dietary behavior. Prevention Science, 2, 15-28.

What are your personal anticipations, expectations and hopes for 2015, socially, morally and intellectually?

Season’s Greetings and best wishes for the new year!

Marwan M. Obeidat · Hashemite University

My dear friend John,

Thanks so much for the very inviting, extensive answer. For that, my appreciation is profuse! Rest assured, my dear friend, that I'll spare no effort to make sure I'm up to your high expectations of me and to your over kind words!

May the new year be the beginning of every success for all of us and for every human being in the 4 corners of the globe!

Kindest,

Marwan

• Can someone advise me for coding to genetic algorithm for prediction modeling?

genetic algorithm for prediction modeling

Daniel Kovach · Gayatri Vidya Parishad College of Engineering

http://pyevolve.sourceforge.net

• Michael Polacek asked a question in Mood:
What door colors are best to use in an ED room for psychiatric/mental health?

I have read studies that discuss mood and color in psychiatric settings, but often the study is of a person and the color which does not take into account the many other variables experienced by someone in the emergency department.  There are studies of other rooms, such as used during therapy or in the general milieu.

I'm looking specifically for door color since our rooms are and will always be laboratory white.  I'm thinking that a great study would be to have at least two rooms with different colored doors and see which one the person (in acute psychiatric distress) chooses indicating a perception of safety.

I am going to present a seminar on this publication. How I can cover whole topic? Which important points I have to include in my presentation?

Hello Professor,
In my university, I have to prepare and present a seminar on this publication and it is very important for me. I have some doubts regarding presentation. Hope you will help me.
Can you please tell me how and which points I can include in my presentation? So, whole publication get cover in my presentation.
Thank yo so much

Regards,
Kiran Singewar

Mary Latela · Sacred Heart University

First, be clear about what is expected of you. What are the parameters of your seminar/presentation - how long, in what setting. If your presentation is to be short (under an hour), then you must first read and outline the article. In addition, are you supposed to summarize the article or analyze it? To summarize and analyze, see the following: http://twp.duke.edu/uploads/media_items/scientificarticlereview.original.pdf
How to Read and Review a Scientific Journal Article:Writing Summaries and Critiques.

I believe you could use some support in your technical writing skills. Best wishes!

Can anyone help with broken line analysis using SPSS?

Please, I need someone to assist in providing the procedure involved in using SPSS to run a regression statistical analysis involving broken line. I need to establish the breaking point (Maximum value) for a relationship between level of inclusion of methionine and weight gain in a fish. Thank you.

David O. Akinde · Fusion BioSystems, Lohne, Germany

I am sorry Banjo I had no time to send this for you, i actually did it late in november using a 1-slope broken line model fitted to your data. But as you can see, the goodness of fit is rather poor, so I would prefer the previous quadratic plot instead. All these perhaps are rather late for your analysis. Neverteless thanks for sharing your data.

Why don't we use colchicine to kill directly tumors instead of starving these cells?

As the researchers could change the molecule colchicine to make it inactive in the body until it reaches the tumor and becomes active to break the blood vessels supplying the tumor, and this effect is made possible by enzymes (MMT1) that produce all tumors, and whose function is to break the normal cells nearby, allowing the tumor to spread, why they don't use the molecules that can stop the division and cell function for killing the tumor cells directly.

Massakib Bekkaye · The University of Batna

Thank you Mister Joe Graymer for the informations

Does the protective layer Al2O3 form on the surface of aluminium alloys (such as Al-Zr) like pure aluminium?

Does the protective layer Al2O3 form on the surface of aluminium alloys (such as Al-Zr) like pure aluminium

Bilal Naqvi · National University of Science and Technology

Zr will form oxide preferably in this case because it has more affinity towards oxygen

Is there anyone that has ever been dealing with "Spatial Behavior" in the context of vernacular settlement?

Spatial behavior research has been frequently used in the context of modern settlement, is there any significant difference between research on both context thank you ...

Steven A. Moore · University of Texas at Austin

PhD Candidate Kristine Stifany, at the University of Texas, is now completing her dissertation which examines the spatial relationship between "self-built" educational and housing spaces in Sao Paulo's favellas. Her work will be completed by May.

How can I use EDS for my thin films on several different substrates?

I have Cu2ZnSnS4 films on soda lime glass and Silicium wafer. I choose Si wafer for correct measurement of elemental analysis. In EDS analysis how can I ignore (or remove) Si from spectrum? Is it reliable measurement for other metals' composition. Any other reliable and robust method will be appreciated (not XRF beacuse I have no XRF facility in our lab).

Ahmet Tombak · Batman Üniversitesi

G. Nolze "do not see Si anymore." good solution. Thank you

Is there a contrastive study between the Australian Education System and the Spanish one?

We are doing a contrastive analysis between educational systems of different countries. We are mostly interested in Australian system addressing the instruction of foreign languages. Any other system may be of help, though. Thanks.

Ramon Bassa · University of the Balearic Islands

Perhaps if you look for a PH D in a university of Spain (internet), you can found it.

Does anybody have articles on Genetic Algorithms?

Evolutionary programming.

Daniel Kovach · Gayatri Vidya Parishad College of Engineering

I published an article recently on the topic.  It is a deeply theoretical treatment of the subject which essentially proves that life is a form of intelligence as per the framework I've introduced. You can download it here:

http://arxiv.org/abs/1412.6144

Also, this book is somewhat of a classic in my opinion:

For a more practical approach, I would take a look at PyEvolve

http://pyevolve.sourceforge.net

which is a framework for genetic programming in Python.  I find Python the most effective language for these types of things, but that is highly contentious.

• Is there any way to determine the eigenvalues of A ^ TA?

We know that A^TA is a semi-positive definite one and we want to know its nonzero eigenvalues, and we also have A^2=A.

Wiwat Wanicharpichat · Naresuan University

Singular values are often confused with eigenvalues. However, the singular values $\sigma_{k},$ $1\le k \le n,$ of $A$ are in fact the square roots of the eigenvalues of $A^{*}A.$ If $A$ happens to be symmetric positive definite, $A^{T}A = AA = A^{2},$ then indeed the singular values of $A$ are the same as the eigenvalues of $A$; but in general they are not the same.

• Aakash Pandita asked a question in Protocols:
What is the best diagnostic and management protocol for a PPHN baby?

EVIDENCE BASED?

Has there been any further comment since 1922 on the Huygens method Einstein and Eddington used to calculate light bending in general relativity?

In 1920 Eddington published a book Space, Time & Gravitation on general relativity which included an ingeniously simple derivation of light bending using general relativity.  The book may be found at a link below, and the explanation is on page 99.  Einstein used essentially the same explanation in The Meaning of Relativity published in 1922 (also linked below), in the vicinity of equation (107).  A coordinate transformation is made so that coordinate light speed is isotropic and Huygens bending, also known is the Fresnel principle, is applied.  The answer is taken at face value without re-transforming coordinates.

Using a graphical analysis of Huygens bending, I concluded that it is not coordinate independent.  See image attached.

Has there been any discussion of this method since 1922?  Is it still considered correct?

Robert Shuler · NASA

It doesn't actually matter.  It does not even matter if the EP is valid or not.  All that matters is that the math and derivations are consistent.  That if one accepts the EP it should either:

• A. lead to a clear contradiction (no one has really claimed this)
• B. leads to a theory of gravity in which the EP is completely valid and explains everything it should explain.

The case B has been ambivalent for 100 years without anyone invoking clearly case A.  All I have done is add (considerable) weight to case B.  I have shown that accepting equivalence leads to a gravitational theory in which one must choose an additional relation for the variation of acceleration from place to place, which determines the exact curvature coefficients in the metric.  But the presence of the coefficients and even their general magnitudes, and that one has to be the reciprocal of the other, is required by equivalence.  If you choose other coefficients, I can show it leads to case A.

Since these coefficients are all that is required to calculate full light bending (in fact without the further determination of the variation from place to place they are quite close enough using either the potential or acceleration laws of Newton), then equivalence explains full light bending.  Even if one cannot draw it with the simple falling diagrams.

QED

Can structural dialectology be used for investigating morphological, lexical and grammatical relations?

Can structural dialectology be used for investigating morphological, lexical and grammatical relations?

Ramon Bassa · University of the Balearic Islands

Why not if you use a linguistic method!

• What is the role of surfactant in meconium aspiration syndrome?

what is the evidence?

How can I get rid of my fungal contamination in my alga culture?

Recently i am growing algae in petri dish..during growth i found fungus or yeast..why? I used BG 11 media..should i use antibiotic?what to do ?

plz suggest solution for preventing growth of yeast or fungus ?or other relative precaution for making BG 11 medium.thanks

Harshad Rathod · Indian Institute of Technology Roorkee

thanks all of you for your kind suggestions..will look forward.

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

No body claims that he had a Time travel . Moreover, according to second thermodynamic law, entropy is increasing. Both are in agreement with the current physics  principles. However when I receive the first news that is opposite of presnt laws but comes to reality then I think about this anomaly. However it has not happened yet.

Are there any theories that would be useful for researching the relationship between art and language?

I am interested in doing a research about the effect and role of language in art mainly concentrating on modern/contemporary Asian art (particularly Mainland Chinese and Taiwanese). I would like to look at this question more from the perspective of linguistics than the fine arts one. Any recommendations, suggestions or references regarding "art and language/text" topic would be very appreciated.

Ramon Bassa · University of the Balearic Islands

• Xiao Feng asked a question in Water Sampling:
How to convert Chlorinity to Salinity?

One paper mentioned Chlorinity of water sample = 300 mg/L. But another paper cited the first paper but interpreted as Salinity = 2‰.

I found that the unit of Chlorinity is usually g/Kg, or written as ‰.

I also found a relationship that: Salinity(‰) = 1.80655 x chlorinity

----

I tried to convert Chlorinity (300 mg/L) to Salinity, but I did not get 2‰. So am I right or wrong?

300 mg = 0.3g

1L* 1.025 kg/L =1.025kg

Chlorinity =  0.3 g/1.025 kg = 0.29‰

Salinity = 0.29‰ * 1.80655= 0.5 ‰

• What are the values of the ionic conductances (Na, K and Cl) in case of an inhibitory neurotransmitter, preferably GABA (alpha-aminobutyricacid) ?

The values of the ionic conductances for excitatory neurotransmitters can be found from the paper published by A. L. Hodgkin and A.F. Huxley. Are the values same for inhibitory neurotransmitters? Is yes, then what is the difference?

Erick Arguello · Simon Bolívar University

Hi Bijeet,

I think the values of ionic conductances are the same. The only difference will be at postsynaptic level. At an excitatory synapse, neurotransmitter opens channels in the postsynaptic membrane that are permeable to cations, principally Na+ and K+. On the contrary, the direction of IEPSP is outward; an outward Cl− current represents an influx of the negatively charged Cl−, which will hyperpolarize the cell. Another possibility is that the inhibitory synapse channel is permeable to K+, with a Nernst potential of −90 mV. An increased permeability to K+ can bring the membrane potential close to the Nernst potential for K+ and thus hyperpolarize the cell.

• Ranjan Sarmah asked a question in siRNA:
Is there any standard Plant siRNA dataset?

Like Huesken dataset which is for mamalian, is there any other standard plant dataset available????

• Aron Roland asked a question in Grid:
Can anybody give some good reference howto compute 3rd and 4th order spatial derivatives on unstructured triangular grids?

for the higher order extended wave action equation we need to computer higher order derivatives on unstructured grids, any hints suggestions r welcome ...

• Is Alexa Fluor more suitable than DyLight?

"Alexa Fluor® 488 dye conjugate showed a 15–30% better signal-to-noise ratio than the DyLight™ 488 conjugate" - How true is this? Does anyone have any experience that says the opposite? Do Alexa Fluor dyes actually perform better than DyLight dyes?

Steingrimur Stefansson · HeMemics Biotechnologies Inc

Hi Nurul, both dyes are variations of fluorescein.

Companies that sell these fluorescein derivatives with names like  Oregon Green, Tokyo Green, SNAFL, carboxynaphthofluorescein, Alexa 488, FluoProbes 488 and DyLight 488 are all claiming that their fluor is superior in one way or another.

Personally, I cant tell the difference between Alexa and DyLight. Sorry.

• 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.

Prof. Dr. Shahid H. Sheikh · NIDS Treatment & Research Center, Lahore, Pakistan

I don't think children should be exposed to any "Statins".

There are other solutions available.