(Visited 112 times, 1 visits today)FacebookTwitterPinterestSave分享0 The national park signs may need updating.Arches National ParkNatural sandstone arches occur in many parts of the world, most notably in Arches National Park in eastern Utah. Visitors, upon reading the confident-sounding interpretive signs describing arch formation, might be surprised to learn that the origin of these structures is not fully understood. In a recent paper in Nature Geoscience, researchers from the Czech Republic who ran some new lab experiments imply that prior theories are incomplete, if not wrong:Weathering and erosion of sandstone produces unique landforms such as arches, alcoves, pedestal rocks and pillars. Gravity-induced stresses have been assumed to not play a role in landform preservation and to instead increase weathering rates. Here we show that increased stress within a landform as a result of vertical loading reduces weathering and erosion rates, using laboratory experiments and numerical modelling. We find that when a cube of locked sand exposed to weathering and erosion processes is experimentally subjected to a sufficiently low vertical stress, the vertical sides of the cube progressively disintegrate into individual grains. As the cross-sectional area under the loading decreases, the vertical stress increases until a critical value is reached. At this threshold, fabric interlocking of sand grains causes the granular sediment to behave like a strong, rock-like material, and the remaining load-bearing pillar or pedestal landform is resistant to further erosion.The new theory is summarized in the BBC News. In addition, Smithsonian Magazine has an embedded video clip of the experiments.In the authors’ view, gravity is the arch-hero, not the arch-villain. The gravitational load causes a kind of self-organizing system: the sand grains lock together in the pillars, resisting erosion. Eventually, of course, erosion wins, and the structure falls. It’s not clear if they can generalize this process to all arches. They experimented with a particular sand in their home country. “Critically, the sandstone from Strelec doesn’t contain cementing minerals that help bind the sand particles together,” the Smithsonian article says. “Instead, the authors found that the stress put on the sandstone causes minerals to interlock and hold the rock together.” It sounds like this is the best-case scenario to test the idea, because cementing materials would presumably increase the resistance to erosion in the pillars. Whether this applies to the Entrada Sandstone in Arches National Park is not clear; it also would not seem to apply to granite arches, as pictured below.Mobius Arch (granite) by David CoppedgeWhatever its merits, this new theory turns the old one on its head: “We should not say erosion or weathering carved the forms, as it was the stress field which give the forms the shape,” lead author Jiri Bruthans asserts in the Smithsonian article. “Erosion processes are mere tools controlled by stress.” The BBC quotes Bruthans comparing the stress field to Michelangelo. “The stress field is the master sculptor – it tells the weather where to pick.”Not much is said in any of the articles about how long it takes for arches to form. The Smithsonian says:The Czech team wanted to take a different approach. While doing fieldwork in Strelec quarry in the Bohemian Cretaceous Basin, they noticed that small arches and pillars—only about 2 feet high at most—formed out of the sandstone over mere months or years, rather than the millennial time scales associated with large geologic architecture.The BBC News, though, without a reference, says “The process had proved difficult to study, because natural slabs of sandstone erode over millions of years.”Landscape Arch, by David CoppedgeCreationists like Michael Oard have shown how just a few centuries since the Flood are sufficient (Creation.com, 2010) to form arches. He quotes secular authors who estimate only tens of thousands of years, not millions, for their formation; in fact, Oard argues, too much time is problematic: the arches should be long gone after even tens of thousands of years. Dr. Andrew Snelling, creation geologist, agrees, discussing sandstone arches briefly in the latest Answers Research Journal from AiG (July 2014). “What the park rangers won’t tell you,” Snelling says, is that 43 sandstone arches have collapsed since 1970. “Their loss is a sober reminder how delicate—and recent—these formations are,” he ends, after providing a Flood model for their formation. “Rapid processes created them and are now destroying them.”The Nature Geoscience paper is not clear on timeframes, so it is not clear the new theory can speak to the age issue. For the huge arches that were not observed forming, one can only estimate, considering variables and unknowns. Did arches form under steady-state processes vs one-time processes (like the Flood)? What were historical rainfall and wind patterns? You can’t look at erosion in a desert today and simply assume it’s always been so slow. It’s possible, in fact, to calculate reasonable upper limits on age of arches by taking conservative erosion rates today, and seeing how far back they can be extrapolated. If those rule out the “millions of years” interpretation, they show old ages to be a philosophical bias, not a conclusion from the evidence.Two other conclusions can be drawn from this story, though. One is the use of arches for design inference. What’s the difference between Landscape Arch pictured above, and the St. Louis Arch? Clearly the former is natural, and the latter intelligently designed. Beyond intuition, how can we tell? Use of such pithy examples can help teachers convey the principles of intelligent design. (Note: Comparing stress fields to Michelangelo is a personification fallacy.)The other conclusion is that scientific theories are at best tentative, especially when they try to speak of the unobservable past. The new theory is partly empirical, because these scientists were able to reproduce some features in the lab. But can one really scale up a small lab model by several orders of magnitude? Other factors might intrude at that level. For what it’s worth, the new theory overturns decades of thought and assumption about how these beautiful structures form, reminding us that science is, at best, a fallible human enterprise. Remember this story when you read the authoritative-sounding National Park signs.
The ways to grow a tech startup company are outnumbered only by the ways to skin a cat.In between multiple rounds of venture capital from investment groups and skin-of-your-teeth bootstrapping, there exists an ecosystem of organizations designed to grow startups with a mixture of business acceleration, development assistance, small rounds of funding (usually just enough to keep Top Ramen on the table), and general advisement. Each organization has its own trademark way of doing things, and here are five that we find fascinating.Y Combinator: From “Babies” to BusinessesThis Silicon Valley-based venture firm is known for attracting some of the youngest technical talent around and molding their inklings into viable companies through a three-month process that occurs twice a year. The hacker-heavy program is headed up by Paul Graham and Anybots founder Trevor Blackwell, both Harvard grads.How They Invest: Y Combinator gives the startups a small amount of money (around $20,000 or less) in exchange for a 2-10 percent share in the company.Startups They’ve Helped: Disqus, PosterousTechStars: Mentors as Far as the Eye Can SeeThis organization began in Boulder, CO, and has recently branched out to a new office in Boston, MA. The business acceleration summer program is best known for its huge, diverse, and truly impressive stable of experienced mentors, who run the range from entrepreneurial rockstars to financial geniuses. We’ve done a slew of video interviews with TechStars folks lately; check them out.How They Invest: TechStars gives startups $6,000 per founder in exchange for roughly 6 percent equity in the company.Startups They’ve Helped: SocialThing, BrightKiteRemarkable Wit: Venture TechnologistsThe Nashville-based offices of Remarkable Wit are basically a sweatshop for greatness with no capital added. This team invests development talent, consulting services, executive expertise, and operations and production labor to get startups up and running. Founded by Emma email marketing alum Marcus Whitney, this organization takes a longer amount of time than a business accelerator to become a true technology partner to the companies in its care. Check out our video interview with Whitney earlier this year.How They Invest: Remarkable Wit invests time and labor – but no capital – in exchange for equity.Startups They’ve Helped: MoontoastSproutBox: More Money, Not Necessarily More ProblemsIn Bloomington, IN, the SproutBox team is taking four startups at a time and pumping around a quarter of a million dollars into each one over the course of ten months. In addition to all that mouth-watering lettuce, the ‘Box is also investing teams and resources. Although they just launched this year, they plan to start a new cycle every three months.How They Invest: SproutBox gives funding and resources in exchange for equity.Startups They’ve Helped: DecideAlready, CheddarGetterLaunchBox Digital: Capital (And More!) in the CapitalThis firm, based in Washington, D.C., offers capital, advisement, and all-important access to investors and press for early-stage startups. Their inaugural class from summer 2008 took nine startups through a 12-week accelerator program with enough seed funding to get them started. Once the program is finished, demo days take place both in the northern Virginia tech corridor as well as Silicon Valley.How They Invest: LaunchBox offers startups up to $20,000 for 6 percent equity in the company.Startups They’ve Helped: ShareMeme, Buzzable jolie odell A Web Developer’s New Best Friend is the AI Wai… Why Tech Companies Need Simpler Terms of Servic… Tags:#start#startups Top Reasons to Go With Managed WordPress Hosting Related Posts 8 Best WordPress Hosting Solutions on the Market
Installing the trussesZach let me stand by the front door rough opening and give the crane operator hand signals. It was a fun way to watch the roof take shape. Once the trusses neared the front door, Zach could signal the crane operator himself, so I was able to get some shots from just outside the construction fence (see Image #2, below).Once the trusses were on, and the guys had a chance to install the final top row of Zip sheathing (up to the bottom of the trusses on the exterior side of the wall), I could move inside to seal all the connections from the interior (see Image #3, below).Because of the cold, the Grace membrane was beginning to lift at the edges in certain spots, so just to make sure it had a nice long-term seal, I went around the perimeter of the house and used a layer of Tescon Vana (3 inches wide) tape to seal the edge of the Grace membrane. Finding the right flashing tapeI tried using rolls of conventional peel-and-stick window flashing membrane, purchased from Home Depot and Mendards, but it performed poorly, even in unseasonably warm temperatures for February in Chicago.I switched to Grace Ice & Water Shield, normally used as a roofing underlayment along the first few feet of roof edge. Because it came on a long roll about 4 feet wide, my wife and I cut it down to a series of strips that could more easily be applied to the wall-top plate connection. While the sun was out, the Grace membrane worked fairly well, especially when I applied pressure with a J-roller.Unfortunately, the sun and warmer temperatures didn’t stick around long enough for me to finish. Within hours, it was back to rainy, gray, and cold — typical Chicago winter weather for February. When the weather went gray and cold again, we started to use a heat gun to warm up the Grace membrane, which had turned stiff and nearly useless in the cold.After wasting a lot of time and effort trying to preheat the Grace membrane before installing it, I finally relented and switched to the much more expensive (but also much more effective) Extoseal Encors tape from Pro Clima. Where the Grace membrane lost virtually all of its stickiness, the Extoseal Encors stuck easily and consistently, with the J-roller just helping it to lay flatter and more securely.It was a case of trying to be penny wise but ending up pound foolish. Looking back, I would gladly pay an extra $300 in materials to have those hours of frustration back (including the time it took to run to the store and buy the heat gun, which turned out to be ineffective anyway).After finishing sealing the Zip sheathing-top plate connection on all the outside perimeter walls over the weekend, it was time for the trusses to be installed. Once the wall assembly details were figured out, and our ceiling setup detailed, the transition between the two became the next challenge. In other words, how to carry the air barrier over the top of our exterior walls.I found an article by Chris Corson published by The Journal of Light Construction to be very helpful.Using a waterproof peel-and-stick membrane to wrap over the top of the wall (going from exterior sheathing — in our case 7/16-inch Zip sheathing — to the interior side of the top plates) seemed like the easiest way to maintain a continuous air barrier at the wall-to-roof junction. The membrane would also have a nice air sealing gasket effect after the trusses were set in place.I also found this excellent Hammer & Hand video on YouTube (one of their many helpful videos).By being able to carry the Zip sheathing up above the top plate of the wall, hugging the bottom of the trusses, meant our 4 inches of Roxul Comfortboard 80 over the Zip sheathing would rise above the top of our walls, so that thermally we would be protected from the exterior walls to the attic, which will be filled with 24 inches of blown-in cellulose.That makes our thermal envelope continuous for the whole house: under the basement slab to the exterior of foundation, to the exterior walls, to the attic (except for one small gap at the footing-slab-foundation wall connection, which I talk about in a separate post).A high R-value wall meets up with a high R-value attic, with no thermal bridging, making our thermal layers continuous. When this is combined with an equally airtight structure, conditioned air cannot easily escape, resulting in a significantly lower energy demand for heating and cooling (and therefore lower utility bills), and added comfort for the occupants. Installing shinglesWe had to wait for shingles for quite some time. First we had to fire our GCs, and then I had to find a roofer and a plumber (to make penetrations through the roof before the shingles went on). But before the plumber could even start, I had to get the Intello installed on the ceiling. And even before that, I had to figure out the insulation baffles, which I’ll talk about in a separate post.It took a while to find a roofer, since they would have to make three separate trips for a relatively small job. The first trip was just to set down the Grace Ice & Water Shield at the edges of the roof, along with a synthetic roofing underlayment (the consensus was that typical roofing felt wouldn’t hold up to long-term exposure). As it turned out, it took weeks before the plumbers made their penetrations through the roof sheathing (literally the day the roofers showed up — a long, horrible story in and of itself that I’ll save for later).The second trip out for the roofer was to install the shingles on the roof of the house. The third trip was to install shingles on the garage roof, but that could only happen after the Roxul had been installed on the exterior of our Zip sheathing (in order to make a proper sealed connection between the wall of the house and the garage roof).There weren’t many roofers willing to work with our unique Passive House sequencing, but Peterson Roofing was kind enough to take it on.Unfortunately, the day after the guys installed the Grace membrane and the synthetic underlayment, we had a cold, blustery day. Once the wind grabbed the Grace membrane, the membrane rolled up on itself, turning it into a real mess (see Image #4, below).Because of our recent past bad experiences with general contractors, I just assumed I was on my own, so I spent a couple of hours putting down new layers of the Grace membrane. When Peterson roofing found out, they were shocked I did it myself, and assured me I could’ve called them and they would’ve come back out. We were so used to people not following through, that my low expectations meant it didn’t even occur to me to call them. BLOGS BY ERIC WHETZEL A Light Down BelowKneewalls, Subfloor, and Exterior WallsLet the Framing BeginDetails for an Insulated FoundationThe Cedar Siding Is Here — Let’s Burn ItAn Introduction to a New Passive House Project RELATED ARTICLES Martin’s Ten Rules of Roof DesignAll About Attic VentingQuestions and Answers About Air BarriersAirtight Wall and Roof SheathingIs OSB Airtight?Navigating Energy Star’s Thermal Bypass Checklist Editor’s note: This post is one of a series by Eric Whetzel about the design and construction of his house in Palatine, Illinois, a suburb of Chicago. The first blog in his series was called An Introduction to a New Passive House Project; a list of Eric’s previous posts appears below. For more details, see Eric’s blog, Kimchi & Kraut. Saving a few bucks on roofingWe initially were going to use CertainTeed’s Landmark TL shingles, which mimic a cedar shake shingle profile, but Armando from Midwest Roofing Supply in Schaumburg, Illinois, was kind enough to walk me through the options available. Because our roof isn’t steep, only the neighbors from their second-story windows would get to appreciate the effect. He recommended we save some money, while not giving up on quality or durability, and go with the Landmark Pro product.The shingles went on quickly since we have a relatively small and simple roof (see Image #5, below). In addition to the aesthetic leap that the shingles contributed to the appearance of the structure, it also meant I didn’t have to go around cleaning up the subfloor every time it rained.Although the synthetic underlayment worked pretty well at keeping the rain out, if there was significant wind combined with rain, the water easily found its way under the underlayment where it could then drip and fall on the subflooring below. It was pretty depressing to show up to the job site after a hard rain knowing I was going to spend the first hour just cleaning up and looking for leaks.
Thirteen students of the Central University of Haryana (CUH) in Mahendergarh were suspended on Thursday for allegedly creating “hindrance in the smooth functioning of academic and administrative functioning of the university”. The suspended students, including 11 BTech students, and others have been on strike since the past 10 days against lack of infrastructure and staff in the School of Engineering and Technology.Misbehaviour alleged The suspension came a few hours after the agitating students — who were protesting against alleged misbehaviour by security guards with female students on Wednesday night — prevented Vice-Chancellor R.C. Kuhad from leaving the premises in his car. They claimed the security guards used force on Wednesday to disperse students, including women, who were holding a peaceful protest outside the university’s Academic Block. They added that the guards also tore posters, prompting hundreds of students to hold a protest all night. The agitating students alleged that varsity officials misbehaved with them on Thursday and locked the building from inside to prevent them from entering the premises to drink water and relieve themselves.‘Baseless claims’Dismissed as “baseless” the allegations of misbehaviour by the guards, CUH spokesperson Shailender Kumar accused the students of manhandling the V-C. He claimed CUH had agreed to meet their demands in a time-bound manner and a notice in this regard was already circulated on April 15. Lack of facilitiesThe students are on strike since April 9, alleging that two years after the School of Engineering and Technology was established in 2016, it still lacks minimum facilities like laboratories, building and regular staff. The School offers BTech in four disciplines. However, a student of BTech (electrical engineering) said promises made by the administration were hollow. “We want a letter signed by the V-C himself with a promise to meet all our demands in a time-bound manner. We believed the verbal assurances of the V-C last August but nothing happened. How can we believe the administration that laboratories will be ready in three months when construction of building is yet to start?” said the student. CUH Finance Officer Sanjeev Kumar said the university’s notice to meet the demands of students in a time-bound manner had the approval of the V-C and was signed by the Registrar. “It seems that some people are instigating the students. The students seemed satisfied after a marathon meeting with the V-C on Wednesday but were instigated into continuing the protest. They are coming up with new demands every other day,” said Mr. Kumar.He added that approval of the All-India Council for Technical Education (AICTE) was not required for BTech courses as the university was autonomous body and received grants from the University Grants Commission.
Union Minister of Railways and Commerce Piyush Goyal on Thursday termed the current economic slowdown as just a passing phase and said that efforts being taken by the government only showed that it cared.Reacting to former prime minister, Dr. Manmohan Singh’s views on the economic slow down the country is facing, the Union Minister said that he was surprised to know that Dr. Singh was saying that the BJP government was failing in handling the economy. “The country gave Dr. Singh, an eminent economist, the opportunity to run the country for 10 years. But they [UPA government] damaged the entire economic system. It was during their tenure that reckless bank loans messed up the banking sector, prices of commodities soared up, Mumbai faced a major terrorist attack and the government could not face the public,” he said addressing chartered accountants, industrialists and traders at an Assembly election-related event in Bhayandar. “Before the Modi government came to power people had lost hope and so did not demand anything from the government. But in last five years public has been demanding better facilities because they have immense hope in this government. Even a beggar will beg only in front of someone whom he knows will give him something,” Mr. Goyal said. The last five years have seen 75-78% rise in Foreign Direct Investment (FDI) and it will continue to grow with the efforts the Prime Minister is taking, Mr. Goyal added. “I hope you all remember the double digits inflation we faced during the United Progessive Alliance government. Fiscal deficit was as high as 6-6.5% and current account deficit was 4.5%. The country was handed to us with a damaged economy and we have brought about development across sectors,” he said. Talking of the steps by Union Finance Minister Nirmala Sitharaman to revive the economy, Mr. Goyal said, “ours is a responsible government. The efforts being taken show that the government cares about the economy.”
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