Wikipedia:Reference desk/Archives/Science/2015 September 23

= September 23 =

This Watch
Can someone please tell me about [this watch].These don't seem to be "hot digits", or are they? If not,what is the actual system. How it works? — Preceding unsigned comment added by 27.255.173.200 (talk) 17:49, 28 September 2015 (UTC)

Wavelengths from Outer Space
What are the shortest and longest wavelengths that can be meausred (by telescopes, etc.) from outer space? In other words, what is the spectrum of the measurable wavelength from outer space? 80.246.136.222 (talk) 05:17, 23 September 2015 (UTC)
 * Start here: Electromagnetic_spectrum 196.213.35.146 (talk) 06:21, 23 September 2015 (UTC)


 * The shortest wavelengths that we can measure from space are cosmic gamma rays – the High Energy Stereoscopic System can see gamma rays with an energy of over 100 TeV, which is equivalent to a frequency of 2.4×1028 Hz, or a wavelength of 1.24×10-20 m. Ultra low frequency light is harder to measure from outer space, since there are huge amounts of Earth-based noise at these frequencies. The Demeter satellite can see as low as 10 Hz, but that's pointed at the Earth itself. This paper suggests that the lowest frequency/longest wavelength that can be used in radio astronomy is currently 30 MHz (10 metres). There are (very early) plans to go further, but they would need to be space-based (since the atmosphere blocks low frequencies) and would have to be an array (since it's very difficult to put an antenna large enough on a single spacecraft). Smurrayinchester 10:44, 23 September 2015 (UTC)
 * See Jupiter which uses frequencies down to 20 MHz. And also see Grote Reber where radiotelescope frequencies below 1 MHz were used in a square kilometer array at Bothwell, Tasmania. LOFAR detects down to 10 MHz. The top frequency end is described in Very-high-energy gamma ray, where photons cause flashes of light in the atmosphere. The Earth's magnetic field will prevent much higher energy photons from reaching the Earth by way of photon-photon scattering. Graeme Bartlett (talk) 12:00, 23 September 2015 (UTC)


 * If we interpret "outer space" to include Earth's magnetosphere, then very low frequency radio is commonly detected from that region. Among the many signals are whistler mode waves; dawn chorus (as the magnetosphere warms up from solar radiation, each time it comes out of Earth's shadow); and low frequency hiss.  These waves are in the range from 1 kHz to 100 kHz; and even lower frequency (longer wavelength) signals can be detected if you have the right equipment.  Perhaps the most notable is 7.83 Hz, an ultra-low frequency radio signal we find on Earth a lot, because it happens to be the characteristic frequency of one light-speed trip around our planet!  In other words, the wavelength is approximately equal to one Earth circumference.
 * Here's an introduction to Very Low Frequency radio science. Nimur (talk) 14:07, 23 September 2015 (UTC)
 * LIGO should be able to detect gravitational waves with frequencies 30-7000 Hz or so very soon. That means wavelengths out to ~10,000 km.  --Amble (talk) 20:09, 26 September 2015 (UTC)

This Watch Can someone please tell me about this watch.These don't seem to be "hot digits", or are they? If not,what is the actual system. How it works? — Preceding unsigned comment added by 27.255.173.200 (talk) 17:46, 28 September 2015 (UTC)

Why is BDD considered separate from OCD?
From my understanding, dysmorphophobia is an undesirable manifestation of the OCD neurotype. Why is it considered separate from OCD? Can you be both "properly" obsessive-compulsive and have BDD? Andrea Carter (at your service &#124; my good deeds) 23:10, 23 September 2015 (UTC)
 * OK - so the relevant article is Body dysmorphic disorder. It says "BDD is categorized in the obsessive–compulsive spectrum.".  Our article on Obsessive–compulsive spectrum says: "recently there is a growing support for proposals to narrow down this spectrum to only include body dysmorphic disorder, hypochondriasis, tic disorders, and trichotillomania".   So as far as I can tell, your assertion that it's considered "separate" from Obsessive–compulsive spectrum simply isn't correct.  OCD is a 'spectrum' condition, from people who are just mildly obsessive - to people who are totally debilitated by the condition, and the symptoms of OCD vary between individuals and may or may not include BDD.  So I can't agree with the premise of your question.  If someone suffers from BDD, they are (per medical definitions) fully OCD. SteveBaker (talk) 03:18, 24 September 2015 (UTC)


 * I read the question as being about the difference between OCD, not OC D spectrum, and BDD. OC D spectrum is a group of disorders, with OCD being one of them.
 * According to this, people with BDD tend to have poorer insight (understanding that recurrent intrusive thoughts they have are irrational) than people with OCD. And "BDD compulsions may have a greater emotional regulation function, rather than anxiety reduction as with OCD". Those differences would affect treatment selection and effectiveness. Other article here, mentioning that significantly more BDD patients are classified as delusional. A small magnetic resonance imaging study found opposite differences in OCD vs BDD patients compared to a healthy control group (leftward vs rightward shift in caudate asymmetry and greater vs reduced white matter volume).
 * This study looked at comorbidity between the two: Lifetime comorbidity rates of BDD–OCD are almost three times higher in samples with a primary diagnosis of BDD than those with primary OCD. There are studies of people diagnosed with comorbid BDD/OCD, so having both at the same time is possible.  Ssscienccce  (talk) 04:30, 24 September 2015 (UTC)
 * I am aware of the idea of the obsessive-compulsive spectrum and that BDD is included in it. I was talking about why consider it separate from OCD itself. So people with BDD and OCDers have difference in neurology and psychology but similarities in behavior? Also, OCD is not just a spectrum, it is extremely diverse within the OCDer themself. Ergo, the same person can have periods of no symptoms and periods of severe symptoms and things in between. Andrea Carter (at your service &#124; my good deeds) 17:45, 24 September 2015 (UTC)
 * The spectrum is the group of diseases that have certain features in common with OCD. I was wrong btw to include OCD, the OC spectrum disorders are the ones different from OCD: body dysmorphic disorder, hypochondriasis, tic disorders, and trichotillomania; at least that is the definition that the OC spectrum disorders workgroup for DSM-V used.
 * Before DSM-V, OCD and the spectrum disorders weren't even in the same category: DSM-IV put OCD under anxiety disorders, BDD under somatoform disorders. ICD-10 places BDD (F45.22) under Hypochondriacal disorders (F45.2) which is classified under Somatoform disorders (F45), while OCD is separate (F42).
 * DSM-V groups OCD and the OCSDs together under OCRDs (OCD and related disorders), but they are still considered separate conditions; BDD is not a symptom of OCD.
 * "DSM-V contains a number of changes with respect to obsessive-compulsive disorder and related conditions (OCRDs): the chapter includes obsessive-compulsive disorder (OCD), body dysmorphic disorder (BDD), and trichotillomania (hair-pulling disorder). Second, the chapter includes several new conditions, including hoarding disorder and excoriation (skin-picking) disorder. 
 * The new chapter on OCRDs reflects growing data that OCD differs from the anxiety disorders on a number of diagnostic validators, and that there are important phenomenological and psychobiological overlaps between OCD and a number of related conditions [19]. At the same time, it is important to emphasize that there are both strong overlaps between OCD and the anxiety disorders, and important differences between the OCRDs. " source Ssscienccce  (talk) 20:08, 24 September 2015 (UTC)