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Function

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Posts posted by Function


  1. Hi guys

    For a case presentation in neurosurgery, I'm talking about the Jannetta procedure, in which, in patients with a neurovascular conflict between a cranial nerve and an offending vessel (mostly an artery compressing the nerve and pulsating against it), a sponge-like matter (Teflon, Merocel ...) is surgically inserted between the nerve and the vessel.

    I'd like to briefly talk about how the sponge absorbs most of the pulsatile energy/impact of the vessel, preventing energetic transmission to the nerve. I can't seem to find, however, a physics model explaining this.

    Does someone have a good explanation on how sponge-like matters absorb kinetic energy and prevent transmission of most of that energy past itself?

    Thanks!

    Function


  2. 19 hours ago, studiot said:

    The difficulty comes (as so often) in the crossover grey area where the sufferer is  for instance imagining plots against him or her.
    This involves both the sufferer and the outside world together.

    During my psychiatry internship, most psychotic delusions (and also delusions in, for instance, major unipolar depressive disorder with psychotic features) were such delusions. The tricky part is identifying whether this delusion or idea can be contradicted to the patient, or not. For instance, we had one female patient in her 40s, with the undeniable idea (ergo, delusion) that she was having Alzheimer's dementia. This made her "normal" major unipolar depressive disorder one with psychotic features, making her immediately eligible for electroconvulsive therapy. The delusion became more of a deniable idea as time progressed.

    21 hours ago, StringJunky said:

    You can have a hallucination and know it's not real, which I wouldn't class as a psychotic event but maybe that's not the expert view.

    I think this is still a psychotic feature. Not knowing it's not real, that is, acknowledgeing the hallucination as something real, to me, is a delusion. But I'm not sure as to what guidelines and such state about this.


  3. 1 hour ago, StringJunky said:

    I suppose one difference is that schizophrenia describes a persistent illness and psychosis describes a symptom, which may be transient or not.

    Actually, schizophrenia is one of the "psychosis spectrum disorders", and "psychosis" as such is more of a syndrome, rather than a symptom in itself. A psychosis is an event or episode characterised by either hallucinations, delusions, very chaotic or catatone behaviour, inconsistent speach, or negative symptoms. For schizophrenia, at least two of these "psychotic" characteristics should be present (the "A criterium" for schizophrenia) for a duration of at least 6 months. Comparably, schizophreniform disorder is basically the same, but lasts between 1 month and 6 months.


  4. In the tertiary care centre where I had my internship, yes, they did, as should be done quite routinely to exclude large organic causes (such as acquired brain injuries) for their pathology.

    Here, it's important to not that it's a tertiary care centre we're talking about. As a GP, you shouldn't have MRI scans done of anyone seeing you for depression ...


  5. I do not feel like citing the correct references, but as a matter of fact, yes. Nearly all psychiatric illnesses have organic impact on the brain. And not a good impact, for that matter. During my internship in psychiatry, I observed a lot of MRI scans of people admitted with depression, psychosis, bipolar disorder ... 

    1 thing they had in common: white matter lesions.


  6. 1 minute ago, Prometheus said:

    Does that mean you have been performing multiple hypothesis tests on various peaks? Did you correct for type 1 error inflation, it might be that the finding is erroneous. 

     

    Could you recommend some studies that look at this?

    Concerning type 1 errors: each patient had received a MR spectrum. Each spectrum had some characteristics (11, to be precise, of which 1 was categorical, the other ones continuous), which were all subjected to Shapiro-Wilk (in each subgroup per comparison), and variables with allegedly nonnormal value distributions were log-transformed, and the test was run again. And then, all variables were compared each time between 2 distinct groups (e.g., high-grade tumours v. low-grade tumours). I applied a Bonferroni correction in post hoc tests where more than 2 tumour categories were present (e.g., grade I v. grade II v. grade III v. grade IV), or when the categorical variable (which had 3 categories) turned out to be significantly different between any two (or more) groups. Post hoc chi-squared or Fisher's exact tests were then run, with Bonferroni correction applied to the significance level.

    For the other analyses, there was no need for type 1 error correction, as one could interpret each comparison to be a separate "study". Additionally, no variables were ever combined into one predictive model. That would have led me too far.

    I'll look for some articles that are representative for in vivo MR studies.


  7. 10 minutes ago, Prometheus said:

    True.

     

    That's quite possible, non-parametric tests generally have less power meaning you are more likely to erroneously accept the null hypothesis. Is there a difference between groups when considering the entire spectrum?

    Is there any existing literature out there looking at the similar things?

    There are differences in other parameters within comparisons of other groups, but for this one group–group comparison, only this variable differs significantly.

    I already implemented everything that’s usually used as parameters in MR spectro in human brains, but thought of ‘designing’ new parameters.

    Edit: after all, I aimed not only to confirm what is already known, but to develop some more unusual variables, as we are in search for optimisation of noninvasive diagnostic methods in tumour assessment


  8. 5 minutes ago, Prometheus said:

    What information is contained in the angle between two peaks? What's the reason for not looking at the entire spectrum?

    Could you not just measure the angle such that your protractor, so to speak, is aligned vertically, so that 2 peaks of the same height measure 90 instead of 0? This way all your angles will be bound between 0 - 180.

    Might be simplest just to stick to a non-parametric test.

    I am looking at the entire spectrum, but certain frequency peaks represent very distinct metabolites.

    Change in protractor direction, would that actually not be exactly the same as adding 90 degs to every measured angle post hoc?

    And that’s the stupid part: a nonparametrical comparison of the original angles does not differ significantly between 2 groups, whereas the Briggs log of the angles + 90 degs does. And as my thesis actially focusses on tumour group classifications, I wouldn’t just consider this as a methodology designed “just to find something significant at one point”, but as a methodology to find and describe class predictors. First step in such process is assessing differences in parameter distributions between both groups ...


  9. Log and square root transformations are common transformations in statistics for variables that are nonnormally distributed, hoping to achieve normality in their log- or root-transformed variants. Which I got.

    IBM argues that it is possible to "add a constant big enough" to all values, such that no value is negative or zero, and then apply log transformation.

    An advantage to this method would be that simply adding a constant to each value does not alter variance amongst variable values.

    The situations you present are highly unlikely. We're talking about proton NMR spectroscopy of some in vivo metabolites. Achieving the situations you suggest are nearly impossible, as the peaks themselves will just stay where they are, and only chance in amplitude, not in frequency/chemical shift, which is displayed on the horizontal axis.


  10. Because that's how I defined my angle.

    It's always defined as the angle the line (or, if you like, vector) from the first to the second peak makes with a horizontal line. I wouldn't have liked working with (360° - (negative angle value)) to substitute the negative angles, as then I would have to conclude that the second situation would have a larger angle, which, according to the definition I gave to that angle, is absolutely not the case. The sign of the angle is inherently correlated with the characteristic of both peaks relative to one another (first peak higher, or second peak higher).

    The constant arrangement of both peaks on the horizontal axis made me define the angle to be indisputably either greater than -90°, or smaller than 90°.

    "Log transform a variable" is performing a natural Briggsian logarithm on all its values, and saving the results as values of a new variable.

    fig.png


  11. Hello everyone

    For my thesis, I'd like to log transform a variable that represents a certain angle between 2 peaks on a curve.

    The problem, of course, is that this angle can be negative.

    As no angle is smaller than -90°, would it be allowed to add 90° to all angles, and log transform the results into a new log-transformed variable?

    Thanks

    F


  12. Hello y'all

    In my thesis, I have this variable, which is expressed in a percentage (%). It's not an option to, e.g., display 20 % as 0.20, since that is absolutely not common for that variable.

    Now, this variable does not satisfy the conditions for parametric testing. However, its square-root variant does. But if I report both this variable, in %, then do I have to change the "unit" (which in itself is demensionless) to something else than %?

    Now I would report:

    • Mean Var ± SD - %
    • Mean VarROOT ± SD - %

    But I'm not sure if this is quite right.

    After all: e.g., in the case of 20 %, I took the root of 20, and not of 0.20.

    So ... sqrt(20 %) = sqrt(20) * sqrt(0.01) = 4.47 * 0.1 = 0.447 ~ 44.7 %

    And sqrt(0.20) = 0.447 ~ 44.7 %

    But erm ... Is there a symbol for 1/10? Because now I see that I would incorrectly report 4.47 % (since I only rooted 20 without the %) instead of 44.7 %.

    Thanks

    F


  13. Hello everyone

    During the last sleepless night, some thoughts crossed my mind, and I wanted to share them with you and ask your opinion/points of view regarding them.

    The idea would be that the human brain maps, registers, and saves every single location a human being has ever been, and that, should we have the means to do so, a "route" could be mapped for every human being, from the moment they were born, until the moment they died.

    Useless, of course, but I wondered whether this could be the case.

    After all, our vestibular systems start working quite early; as do our memory circuits. Could it be possible that, from the moment your vestibular system was active, it would register any acceleration across and around any axis, the duration of the acceleration, and that your brain would register the duration of absence of acceleration, until further acceleration or deceleration occurs?

    For example: a child sits on a chair. It stands up (acceleration in both ventral and cranial directions), turns right (rotational acceleration) for 90°, starts walking (again an acceleration), turns 90° back to the left (rotational acceleration), and sits down on another chair (acceleration in dorsal and caudal directions).

    The idea here would be that the vestibular system detects any acceleration and deceleration (which are not mentioned here), the duration of an acceleration/deceleration, and that your brain could register the duration of absence of acceleration. Like so, it would theoretically become possible to reconstruct the path the child has done: ventrocranial acceleration and steady movement, stop, rotational acceleration and steady movement, stop, ventral acceleration and steady movement, stop, rotational acceleration (or deceleration when compared to the other rotation) and steady movement, stop, dorsocaudal acceleration (or ventrocranial deceleration) and steady movement, stop.

    I don't know if it's clear what I mean, but if this were indeed the case, to me this would sound like the positional path of every human could be retrieved and mapped, from the moment they were born, until the moment they died, since every position we've been in could be explained in function of all acceleration, decelerations, and steady movements we've done in our lives.

    This is nothing more than a thought experiment, of course, and yields not much practical consequences. But I was wondering whether you would think this would be plausible, or rather far-fetched and unlikely, due to limited storage capacities within our (spatial) memory ...

    I was also wondering whether this might contribute to so-called déjà vus. Indeed, one may experience a déjà vu based on what one sees or hears or whatever; but could a pure spatial déjà vu also be experienced purely by means of our vestibular system and memory? As if our brains would understand that, if we've been to B (from point A) before in our lives, and now we take a route to the same point B, but from another point (C), the combination of vestibular activity and duration of steady movements would lead us indeed to this point B?

    Regards

    F


  14. 34 minutes ago, studiot said:

    As to Feynman's comment;

    If we regard an electron as a (charged) particle then it is subject to Earnshaw's theorem that states it is impossible for two or more charged particles to remain in static equilibrium, without external restraint.

    So if there is more than one charged particle in a system they  must be in perpetual motion.

    Greetings! Do electrons and protons lose energy over time, as would a magnet lose its "magnetic strength/power" over (long) time?

    If not, then isn't their perpetual motion at variance with the laws regarding conservation of energy?


  15. Welp, I can't really remember why the hell I baptised myself "Function". Guess I liked maths at the time. Yup. Liked. I would still like it, if I hadn't forgotten even how to sole the easiest integrals. But hey, medicine and maths may start both with an "m", but that's about the only thing they have in common. After all, I didn't (and still don't) have the time to adequately maintain my knowledge and skills in maths. I regret, however, that I forgot most of the physics we were taught; I'm actually planning on re-learning physics when I get the time.

    But I'm quite fond of brain tumours. Hence the avatar.


  16. Hello everyone

    Just to make some things clear:

    • Everything mentioned in here is mentioned from a scientific point of view and results from personal observations.
    • This thread is not meant to be racist; if anyone feels in a more or less direct way offended by this post, please let me know what can be changed to work towards a solution that works for both parties.

    So I sat on the train today, after spending too much money on some sweets, a little reward to myself for successfully taking the exam on pneumology, haematology, and nephrology earlier today.

    Looking into my candy bag, and picking some sweets, I suddenly noticed a specific odour. An odour that was very well known to me, an odour that I had come to associate with black people over time. Without knowing who sat in my vicinity, I noticed some frizzy afro-american hairs protruding above the seat in front of me; and it was clear to me that the odour was indeed coming from that person. And I have totally no problem with that; I just noticed it and found it remarkable that I could determine the presence of a person of a certain race in my vicinity just by smelling. Above all, I have 2 black nephews and a black aunt and whenever I'm near them, I cannot help but notice the same familiar, typical odour.

    I'm trying to find what correlation can be made between race and body odour, but I only find some shifty fora with discussions that lead to nothing. I'm looking for scientifically validated data and articles that state that indeed different races do have specific body odours.

    Can someone help me in this search?

    Thank you kindly.

    Function


  17. 1 minute ago, Sensei said:

    Oh, I see where was problem.. you exported in CSV, but you have comma as decimal separator, not CSV field separator..

    After replacing comma by dot, then replacing semicolon by comma, it loaded correctly in Open Office.

     

    Ahh yes; sorry, my bad. SPSS has a period as decimal separator, but forgot that Excel is still set in my regional standards (where a decimal separator is a comma)


  18. 1 minute ago, Sensei said:

    Why not you cannot program? Everybody can program..

    It does not look like what you said in the first post, at all..

     

    Not everyone ;)

    And how so?

    I genuinely believe this is "a 10 x 10 table with 10 by 10 variables and in the cells their correlation coefficient" (correlation coefficient being the correlation coefficient of 2 variables).

    So I'd need every possible set of variables, with none of the inter-variable correlation coefficients of the set exceeding, let's say, 0.1.

     10x10.PNG.91179053fd1ff3d0827bcaf6aa3eb27e.PNG


  19. Hello everyone

    Consider a 10 x 10 table with 10 by 10 variables and in the cells their correlation coefficient. Suppose that I want to select every combinatory set of variables that have a correlation smaller than 0.1. Is there a way in, let's say, Excel, or SPSS, to do this?

    E.g., VAR1 has a correlation smaller than 0.1 with VAR2, VAR3, and VAR4.

    VAR2 and VAR3 have a correlation smaller than 0.1, VAR2 and VAR4 too, but VAR3 and VAR4 have a correlation of 0.2

    The resultant sets are (1) VAR1, VAR2, and VAR3, and (2) VAR1, VAR2, and VAR4.

    You can imagine that this gets really complicated for 10 variables of which some have correlation smaller than 0.1 with at least 6 other variables.

    In short: of 10 variables, I need to define every possible set that is made from any combination of variables, of which their inter-variable correlation is less than 0.1.

    How can I do this?

    Thank you very much!

    F.

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