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I want to add a supplement to Suzanka Bett's great answer.Firstly, this is a great question; ion channels are supremely elegant. This is also an ongoing field of research, there are many theories but no conclusive proof yet. The difference in size between [math]Na^{+}[/math] and [math]K^{+}[/math] is one such theory (there is a little more to this). I write to offer some mechanistic insights, more specifically:What exactly is the process of ion selection and how is this achieved? i.e the difference in Pauling radius between [math]Na^{+}[/math] and [math]K^{+}[/math] is 0.38[math]\AA[/math], what features must the channel have to distinguish one from the other.Figure 1: Relative sizes of some ions, from : Pores and Selectivity FiltersNote: this post is limited to voltage gated channelsSelectivity of Sodium ChannelsSelectivity of [math]Na^{+}[/math] channels remain elusive, and these channels aren't as well studied as [math]K^{+}[/math] channels.[math]Na^{+}[/math] ions pass through voltage gated sodium channels (Nav) in a hydrated or partially dehydrated state (it is largely argued that sodium ions pass through in a hydrated state), depending on the dimension of the pore. (The permeability of the sodium channel to orga... [J Gen Physiol. 1971])The ion binding sites of the channel is called selectivity filter (SF).In mammalian Nav channels, there are two rings of selectivity filters. (Molecular model of the action poten... [Proc Natl Acad Sci U S A. 1986])The outer ring consists of 4 charged residues (EEDD or EEMD), and is known to play little role in "ion selectivity" . (Charge at the lidocaine binding site residue Phe-1... [J Physiol. 2007])The inner ring consists of highly conserved residues (DEKA). And this inner ring is hypothesized to play a larger role in ion selectivity. (On the structural basis for ionic selectivity amon... [Biophys J. 1996])As you would expect, there have been many studies exploring sodium ion selectivity, by mutating residues in the selectivity filter. (Analysis of the selectivity filter of the voltage-gated sodium channel NavRh)Studies show that mutating K of DEKA, results in permeability to calcium and potassium ions. And mutating DEKA to EEEE makes the channel selective towards calcium -Calcium channel characteristics conferred on the sodi... [Nature. 1992] (now, is that cool or is that cool?)The binding of sodium ion is known to involve dynamic interactions with both a)water and b)protein residues.One study looking at [math]Na^{+}[/math] selectivity hypothesizes that the distinction between sodium and potassium ions is a combination of (a) pore lining or the selectivity filter and (b) the pores size at the plane of the selectivity filter. (Mechanism of Ion Permeation and Selectivity in a Voltage Gated Sodium Channel )Although [math]K^{+}[/math] can fit through the pore, with a complete hydration shell, it cannot do so at the plane of the selectivity filter, due to negatively charged residues (DE of DEKA).Figure 2: (A) [math]K^{+}[/math] can fit through the pore (B) [math]K^{+}[/math] can't fit through the pore when D or E is present. (C) [math]Na^{+}[/math] comfortably fits through the pore due to smaller size. Image from : Mechanism of Ion Permeation and Selectivity in a Voltage Gated Sodium ChannelThus, the geometrical arrangement of ions, pore lining and water, influence ion selectivity.Selectivity of Potassium ChannelsPotassium channels have been more extensively studied. Roderick MacKinnon's group determined the 3D structure of potassium channels (Structural conservation in prokaryotic and eukaryoti... [Science. 1998]) and were able to explain the selectivity of these channels with biochemical experiments. (The structure of the potassium channel: molecular ba... [Science. 1998]). Again, this is just a theory/hypothesis and not a conclusive proof.The selectivity filter in potassium channels is characterized by a conserved sequence, TVGYG. (Page on nature.com)This sequence is present in the most constricted part of the pathway.Due to the constriction, the ions must be stripped of water molecules before entering the channel.In the channel, the residues of the selectivity filter replace water molecules with polar oxygen atoms.Figure 3: Potassium channel showing conserved sequence and potassium ions, from : RCSB PDB-101Sodium, on the other hand, is a smaller atom, but has a higher energy of hydration, i.e it is harder to pull the waters of sodium:Figure 4 : Sodium and potassium comparison, from : Page on caltech.eduThus the channel is lined by carbonyl atoms of the selectivity filter, and it is geometrically constrained so that only a dehydrated [math]K^{+}[/math] fits with appropriate coordination but the [math]Na^{+}[/math] is too small. Also, [math]Na^{+}[/math] binding is thermodynamically unfavorable. (Page on nih.gov)

Although I’ve never personally met Elon Musk, throughout my years in high tech and startup related business, I’ve met or even worked for a handful of male executives who somewhat remind me of him.Some people love Elon Musk, others hate him and many people outside of the tech worlds have no idea who he is unless they saw him during his guest appearance on The Big Bang Theory in November of 2015."The Platonic Permutation" -- Wolowitz (Simon Helberg, right) THE BIG BANG THEORY, Thursday, Nov. 19 (8:00-8:31 PM, ET/PT), on the CBS Television Network. Also pictured left: Business Magnate and Inventor Elon Musk Guest Stars as Himself Photo: Monty Brinton/CBS ©2015 CBS Broadcasting, Inc. All Rights ReservedWhy Elon Musk May Seem Uncomfortable In His InterviewsNot everyone will agree, but it is my personal opinion the Billionaire Businessman seems uncomfortable during interviews due to some, if not all, of the following reasons:"A Patch, a Modem, and a Zantac" - Pictured: Elon Musk on YOUNG SHELDON, Thursday, Nov. 30 (8:31-9:01 PM, ET/PT) on the CBS Television Network Photo: Darren Michaels/CBS ©2017 CBS Broadcasting, Inc. All Rights Reserved.He’s been heavily attacked on mainstream and social media for a wide range of sins.The attacks on Musk have ranged from his inappropriate tweets to not making enough cars and at times appearing emotionally and/or mentally unstable.As a result of the outcry over his business and personal behaviors, he is probably very uncomfortable being interviewed by anyone he doesn’t completely trust.He’s probably been warned by his legal and PR teams to be very careful how he answers any questions which may further tarnish his image.If I were Musk and I had been attacked as he has been, whether the attacks were warranted or not, I would go deep underground to avoid additional criticism.Musk is famously impatient.On December 17, 2016 while stuck in traffic he famous tweeted:“Am going to build a tunnel boring machine and just start digging.”A man who likes to be constantly on the move, he may find interviews to be boring and a complete waste of his time. Rather than showing his impatience or boredom, he just acts uncomfortable.Musk has famously been quoted as saying:“Focus on signal over noise. Don’t waste time on stuff that doesn’t actually make things better.”He’s completely exhausted from sleep deprivation.In an interview with the New York Times, Musk revealed he frequently logs 120-hour work weeks and doesn't leave the Tesla factory for days at a time.Not only is he too tired to really engage in interviews, he probably secretly wishes he could use the time to take a nap rather than hang out with some random talking heads.Musk has been described as having a famous temper which tends to get him into trouble with some of his comments.Maybe because he’s sleep deprived, or works too many hours, or is exhausted, but recently he got into a famous war of words with one of the cave rescue worked in the recent Tham Luang cave rescue in Thailand.Tech VC Gene Munster of Loup Ventures said that Musk's latest stunt crossed a line."Your behavior is fueling an unhelpful perception of your leadership – thin-skinned and short-tempered," Loup Ventures' Munster wrote in an open letter to the Tesla and SpaceX CEO.He tends to stammer or stutter and is not known to do well in any type of public speaking event.Inc. Magazine in their article: Elon Musk Fails Public Speaking 101. Here's Why We Hang on Every Word (and What You Can Learn From Him) said that“Musk is an unpolished public speaker at the best of times, but in this presentation he seemed more challenged than usual. He mumbles through the important phrase "multi-planet species" so fast that it's difficult to hear correctly.Musk has also been known to stutter and have a hard time pronouncing certain words when he makes presentations, gives speeches or is interviewed by the media.He constantly multi-tasks and runs feedback loops through his brain which may completely distract him during interviews.Musk has said:“I think it’s very important to have a feedback loop, where you’re constantly thinking about what you’ve done and how you could be doing it better. I think that’s the single best piece of advice: constantly think about how you could be doing things better and questioning yourself.”Musk may be so busy thinking about other things or running his feedback loops, he is not actively present during interviews and thus appears awkward or uncomfortable during the conversations.He prefers emails and text to any other type of communication.Musk has famously stated that he prefers to communicate on his own terms with a preference to asynchronous ways of communication via email and text.Musk has said “I do love email. Wherever possible I try to communicate asynchronously. I’m really good at email.”He also makes himself “hard to reach for people outside his company by using an obscure email address.”He’s painfully shy.There have been reports that Elon Musk suffers from social anxiety and general shyness, especially in front of the media or large groups of people.Elon Musk himself has admitted to being painfully shy.He has indicated on Twitter that he may be bipolar although not medically confirmed.In a series of tweets early in November of 2017 week, Musk spoke candidly about stress and his mental health.When asked about his picture perfect online life, Musk responded by saying “the reality is great highs, terrible lows and unrelenting stress. Don’t think people want to hear about the last two.”Musk hinted at being bipolar although stated that there was no medical diagnosis confirming his opinion about his wild mood swings.He’s high or extremely caffeinated or altered in some way.Think about it. The man rarely sleeps.He is very upfront about his excessive work schedule and limited time for sleeping.Musk may either drink a lot of caffeine or take advantage of other herbal supplements of similar to help him stay awake.Of course that is just my personal opinion. I have no knowledge of his personal and private habits whatsoever.I do have a few opinions I won’t share about what would help him, but that’s neither here nor there. I’ll include my private thoughts to him when I get his email.Edit: October 19, 2018User-13673431258413253575 wisely pointed out that maybe Elon Musk is judged on his speaking based upon his South African origins which people in the United States might not recognize as part of the pattern.Manish shared:“ The part on his speaking caught my eye.After watching countless interviews of South African cricketers + forest rangers (of European descent mainly), I’ve felt their English accent is indeed rather distinct.They tend to speak rather fast and gulp down words/parts of phrases, in the process.Also, their tone goes high around mid sentence, suddenly dropping down to barely audible as the sentence ends.Observed this in Musk, and Charlize Theron to some extent.On the other hand, native South Africans speak slower/clearer, with a more even, although undulating tone (say like Nelson Mandela or Desmond Tutu).”Thank you Manish for your insight on how Musk speaks and noting the South African speech patterns for reference. This insight is much appreciated.Asking Elon Musk Why He Appears AwkwardOnly Musk knows for sure why he seems so uncomfortable during interviews.If I can ever figure out his obscure email address I just might email him and ask him.I’ll let you know what he says.

Let us start the history of kashmir from It's name,it is believed that it got it's name after Kashmir valley formation by Kashyapa Rishi ( son of Marichi, son of Brahma) by cutting the gap in the hills at Baramulla (Varaha-mula).Kashmir has more than 5400 years of history and name “Kashmir” means “desiccated land” (Sanskrit: Ka = water and shimeera = desiccate).During Mahabharata era, Kambojas ruled Kashmir during the epic period with a Republican system of government from the capital city of Karna-Rajapuram-gatva-Kambojah-nirjitastava, shortened to Rajapura, which is modern Rajauri.Peer Panjal, which is a part of modern Kashmir, is a witness to this fact. Panjal is simply a distorted form of the Sanskritic tribal term Panchala. Muslims prefixed the word peer to it in memory of Siddha Faqir and the name thereafter is said to have changed into Peer Panjal.History behind name of JammuJammu was founded by Hindu King Raja Jambu Lochan in the 14th century BCE. During one of his hunting campaigns he reached the Tawi River where he saw a goat and a lion drinking water at the same place. The king was impressed and decided to set up a town after his name, Jamboo. With the passage of time, the name was corrupted and became “Jammu“.Authentic sources of Kashmir history are Nilmata Purana (complied c. 500–600 CE) and Rajatarangini (1150 CE).Kalhana’s Rajatarangini (River of Kings), has all the 8000 Sanskrit verses of which were completed by 1150 CE, and chronicles the history of Kashmir’s dynasties from Mahabharata times to 12th century CE (4600 years of history and complete list of Kashmir Kings).During the reign of Muslim kings in Kashmir, three supplements to Rajatarangini were written by Jonaraja (1411–1463 CE), Srivara, and Prajyabhatta and Suka, which end with Akbar’s conquest of Kashmir in 1586 CE.[General view of Martand Sun Temple and Enclosure of Marttand or the Sun, near Bhawan. Probable date of temple AD 490–555. Probable date of colonnade AD 693–729.]List of Kashmir Kings from 3450 BCEThis list and timings are derived from Rajatarangini.1-5. Names not known 3450-3238 BCE1. Gonanda I 3238-3188 BCE2. Damodara I 3188-3140 BCE3. Yasovati (Damodara I’s wife) 3140-3139½ BCE4. Gonanada II (Yasovati’s son) 3139½-3083 BCE5. Parikshit 3083-3041 BCE6. Harnadeva7. Rama deva8. Vyasadeva9. Drunadeva10. Simhadeva11. Gopaladeva12. Vijayananda13. Sukhadeva14. Ramananda15. Sandhiman16. Marahandeva & Kamandeva.17. Chandradeva18. Anandadeva19. Drupadadeva20. Harnamdeva21. Sulkandeva22. Sinaditya23. Mangaladitya24. Khimendra25. Bhimasena26. Indrasena27. Sundarasena28. Galgendra29. Baladeva30. Nalasena31. Gokarna32. Prahlada33. Bambru34. Pratapaseela35. Sangrama chandra36. Larik chandra37. Biramchamdra33. Babighana39. BhagavantaGonanda I was relative of Magadha ruler Jarasandha and contemporary to Yudhishtir. He was killed by Krishna’s elder brother Balarama.His son Damodara I was killed by Krishna and his army. Later Krishna made his wife Yasovati as temporary ruler for 6 months, who was succeeded by her son Gonanda II.This Gonanda II was Killed in a battle with Parikshit (grandson of Arjuna), king of Hastinapura in 3083 BCE.As Gonanda II has no heir, Parikshit took over the kingdom of Kashmir, incorporated it into his empire and handed it over to Harnadeva, who was from his family.From Harnadeva, PANDAVA dynasty kings ruled over Kashmir for 1331 years from 3083-1752 BCE.40. Lava 1752-1713 BCE41. Kusa or Kusesaya 1713-1674 BCE42. Khagendra 1674-1635 BCE43. Surendra (Issueless) 1635-1596 BCE44. Godhara (Another family) 1596-1557 BCE45. Suvarna 1557-1518 BCE46. Janaka 1518-1479 BCE47. Sachinara (His Paternal uncle was Sakuni’s great grandson) 1479-1447 BCE48. Asoka or Dharmasoka (Gonanda Dynasty) 1448-1400 BCEHe lost his kingdom, as Mlechchas occupied it and he fled to forest. His son Jaelauka reconquered it)49. Jaelauka 1400-1344 BCE50. Damodara II 1344-1294 BCE50. Hushka, Jushka and Kanishka 1294-1234 BCE52. Abhimanyu 1234-1182 BCEDharmasoka built Srinagar, capital of Kashmir during 1448-1400 BCEGonanda I was a poet. Dharmasoka, who belonged to the Gonanda dynasty, freed himself from sins by embracing Buddhism and built the city of Srinagar, with ninety-six lakhs of houses, resplendent with wealth.He too was a poet.Dynasty of Gonanada III. From 1182 BCE to 272 BCE – Total 910 years53. Gonanda III 1182-1147 BCE54. Vibhishana 1147-1092½ BCE55. Indrajit 1092½-1057 BCE56. Ravana 1057-1027 BCE57. Vibhishana II 1027-991½ BCE58. Kinnara or Nara 991½-952 BCE59. Siddha 952-892 BCE60. Utpalaksha 892-861½ BCE61. Hiranyaksha 861½-824 BCE62. Hiranyakula 824-764 BCE63. Vasukula 764-704 BCE64. Mihirakula 704-634 BCE65. Baka 634-594 BCE66. Kshitinamdana 594-564 BCE67. Vasunamdana (Poet) 564-512 BCEThis Vasunandana was a poet and author of Samara Sastra.68. Nara 512-477 BCE69. Aksha 477-417 BCE70. Gopaditya 417-357 BCEThis Gopaditya built the temple of Adi Sankara in 367-366 BCE. He founded several temples and Agraharams. He was also a poet.71. Gokarna 357-322 BCE72. Kinkhila or Narendraditya 322-285 BCE73. Andha Yudhistira 285-272 BCE(He was called Andha Yudhistira by the people, because of his having small eyes. In fact he was not blind.)Dynasty of Pratapaditya (272 to 80 BCE – Total 192 years with 6 kings)74. Pratapaditya 272-240 BCE75. Jalaukasa 240-208 BCE76. Tunjina 208-172 BCE77. Vijaya 172-164 BCE78. Jayendra 164-127 BCE79. Sandhimati 127-80 BCEThis 74th king Pratapaditya is mentioned in Rajatarangini as a relative of Vikramaditya, was brought by the ministers from a distant land and placed on the Kashmir throne. He ruled Kashmir from 272 to 240 BCE.Vikramaditya referred to here must be Sri Harsha Vikramaditya of Ujjain from 457 BCE. Kalhana says that this Vikramaditya, the relative of the Pratapaditya was not the Sakari Vikramaditya from 57 BCE.80. Meghavahana 80-46 BCE81. Pravarasena or Sreshtasena or Tunjina 46-16 BCE82. Hiranya 16 BCE – 14 CEThis Hiranya died issueless. He was elder brother of Toramana, who along with his wife and son were in exile.83. Matrigupta 14 – 19 CEHe was sent by Emperor Vikramaditya of Ujjain as King of Kashmir.84. Pravarasena II (Toramana’s son ) 19-79 CE85. Yudhistira II 79-118 CE(This Yudhistira II was contemporary to Salivahana, founder of the Era 78 CE)86. Lakshmana (Narendraditya) 118-131 CE87. Tunjina or Ranaditya (Poet) 131-173 CE87. Vikramaditya 173-215 CE89. Baladitya 215-252 CEKarkota Dynasty Kings of Kashmir90. Durlabha vardhana (Son-in-law of Baladitya) 252-288 CE91. Durlabhaka or Pratipaditya 288-338 CE92. Chandrapeeda or Varnaditya 338-397 CE93. Tarapida or Udayaditya 397-431 CE94. Lalitaditya or Mukatapida(Poet) 431-467 CEThis Lalitaditya built the famous Martanda (Sun) temple in Kashmir.95. Kuvalayaditya 467-468 CE96. Vajraditya or Bapyayika or Lalitapida 468-525 CE97. Prithivyapida 525-569 CE98. Sangramapida 569 CE(ruled only for 7 days)99. Jayapida (Pandit and poet) 569-620 CE100. Lalitapida 620-672 CE101. Sangramapida II 672-729 CE102. Chipyata-Jayapida 729-781 CE103. Ajitapida 781-837 CE104. Anangapida 837-840 CE105. Utpalapida 840-845 CE106. Sukhavarma 845-852 CETotal 17 kings ruled for 600 years[ Martand Sun Temple Central shrine, dedicated to the deity Surya. The temple complex was built by the third ruler of the Karkota dynasty, Lalitaditya Muktapida, in the 8th century CE. It is one of the largest temple complex on the Indian Subcontinent. ]Utpala Dynasty Kings of Kashmir107. Avantivarma 852-880 CE(In his court f1ourished many poets like Anandavardhan, Ratanakara)108. Sankaravarma 880-900 CE(Contemporary to Lalya Sahi, Brahmin king of the Yavanas in Uttara Jyotisha, Divya Kataka and Simhapura, now part of Afghanistan)109. Gopalavarma (minor, whose mother Sugandha ruled) 900-902 CE110. Sankata111. Sugandha112. Suravarma 902-904 CE (all 3 ruled for 2 years only)113. Partha 904-918 CE114. Nirjitavarma 918-920 CE115. Chakravarma (assassinated) 920-934 CE116. Unmattavanti 934-936 CEThese 8 Kings ruled for 84 years.Gupta Brahmin Kings Dynasty of Kashmir117. Yasaskara 936-945½ CE118. Varnata (1 month)119. Sangramadeva (5 months) 945½-946 CE120. Parvagupta 946-948 CE121. Kshemagupta 948-957 CE122. Abhimanyugupta 957-971 CE(Abhimanyu was a minor, ruled by mother Didda or Diththa Devi, wife of Kshemagupta. Didda was contemporary to Bhima Sahi of Kabul, descendent of Lalya Sahi. Didda was grand daughter of Bhima Sahi(Daughter’s daughter)123. Nandigupta (second son of Didda) 971-972 CE124. Tribhuvanagupta (3rd son of Didda) 972-974 CE125. Bhima gupta (4th son of Didda) 974-979 CEAll sons were minors. So, ruled by mother Didda126. Didda or Diththa, herself reigned 979-1012 CE(Didda was daughter of Simharaja of Lohar and wife of Kshemagupta)This Lohar family belongs to the Andhra Satavahana dynasty. This Simharaja, father of Didda, is the son-in—law of Bhima Sahi of Kabul who belonged to the Thomara Dynasty, one of the four Agni Vamsi.These ten Brahmin kings ruled for 76 years.Lohar Dynasty rulers of Kashmir127. Sangramaraja 1012-1027 CEHe is brother’s son of Didda; contemporary to Trilochana Pala of Kabul128. Hariraja 22 days only129. Anantadeva 1027-1062 & 1062-1078 CEAnantadeva was dethroned for few days in 1062 CE, but came back.130. Kalasa or Ranaditya (Pandit and Poet) 1078-1088 CE131. Utkarsha (few days only)132. Harsha 1088-1110 CEThese six kings of Lohar Dynasty ruled for 98 years.Agni Vamsa or Brahma-Kshatra Kings of Kashmir133. Uchchla (few days)134. Sankaraja 1110-1120 CE135. Sussala 1120-1128 CE136. Jayasimha 1128-1148 CEKalhana’s time is 1148 CE.4593-1148 = 345O BCEThat means, from 3450 BCE we have the history of Kashmir for 4593 years and then till today, which is 5467 years.Kalhana’s father was a tributary to the king of Kashmir, besides being the Prime Minister. This family might have been a branch of the Satavahana dynasty.Earliest Neolithic sites in the flood plains of Kashmir valley are dated to c. 3000 BCE. Most important of these sites are the settlements at Burzahom, which had two Neolithic and one Megalithic phases.This proves the history of Kashmir for almost 5000 years.Lohar dynasty (1012–1320 CE) paved the way for foreign invasions of Kashmir. Suhadeva, last king of the Lohara dynasty, fled Kashmir after Zulju (Dulacha), a Turkic–Mongol chief, led a savage raid on Kashmir.Rinchana, a Tibetan Buddhist refugee in Kashmir, established himself as the ruler after Zulju.Rinchana’s conversion to Islam is a subject of Kashmiri folklore. He was persuaded to accept Islam by his minister Shah Mir, probably for political reasons.From the 14th century, Islam gradually became the dominant religion in Kashmir. The Sultans between 1354–1470 CE were tolerant of other religions with the exception of Sultan Sikandar (1389–1413 CE). Sultan Sikandar imposed taxes on non–Muslims, forced conversions to Islam, and earned the title But–Shikan for destroying idols.Later, Mughals (1580s–1750s),[Gateway of enclosure, (once a Hindu temple) of Zein-ul-ab-ud-din's Tomb, in Srinagar. Probable date AD 400 to 500, 1868.]Afghan rulers (1750s–1819), Sikhs (1820–1846 CE) ruled over Kashmir.[Sheikh Imam-ud-din along with Ranjur Singh and Dewan Dina Nath. 1847. (James Duffield Harding) Sheikh Imam-ud-din was the governor of Kashmir under the Sikhs, and fought on the side of the English in the battle of Multan during the First Anglo-Sikh War (1845–46).]Between 1846-1947 CE, there was Princely State of Kashmir and Jammu (Dogra Rule).[The bridge at Baramullah in 1900][Nehru visiting the Women's Militia in 1947-48 with their leader, Begum Zainab. Sankharachrya Hill is visible in the background.][Shown in green is the Kashmiri region of Pakistan (POK). The dark-brown region is a part of Indian-administered Kashmir while the Aksai Chin was annexed by China, the Chinese control being tacitly accepted by Pakistan. Area in the North Kashmir region has been ceded by Pakistan to China.][Children making the famous Kashmiri carpets]Sources:- List of Kashmir Kings since 3450 BCE - History19 Old Pictures Of Kashmir That Will Show You How The Times Have ChangedHistory of Kashmir - WikipediaUnfortunately we don't study all this history in our schools. (coz our education sysytem got distorted since pre-british era)It all looks like a heavenly place has been turned into hell with passage of time.Hope history reverses soon !!