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Topics - Md Kamrul Hasan

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Imagine if the same jacket that warms you up on chilly days would also cool you down on hot ones. Fabrics with “phase-change” properties can do that. And a research team from China now shows that 3-D printing techniques can yield a strong phase-change cloth — one that hides some more tricks up its sleeve.
This new fabric not only helps regulate temperatures, but also conducts electricity. It even resists the radio waves used in Wi-Fi.“The combination of those properties is what’s very intriguing,” says Sergio Granados-Focil. He did not take part in the cloth’s development. But this polymer chemist at Clark University in Worcester, Mass., is familiar with phase-change materials.
To understand the fabric’s phase-change properties, consider the DC Comics’ Metamorpho. This superhero could — poof! — suddenly phase-change his solid body into a gas. Or, when he needed it, become a liquid.
Metamorpho is fictional. But phase-change is very real. Water goes through a phase-change when it freezes or evaporates. In each case, it’s the same molecule — just in different chemical phases. The removal or addition of heat triggers the change between phases. Imagine ice cubes melting into a glass of water. The ice absorbs the water’s heat. That warms up the ice, but cools down the water.
The new fabric’s polymer will change its shape at different temperatures. That’s the phase-change part. In the non-crystal phase, “the polymer chains can move around each other,” notes Emily Pentzer, who did not take part in the new work. This polymer re-crystallizes again as it cools, the polymer scientist explains. Pentzer works at Texas A&M University in College Station.
The Chinese team 3-D printed its fabric using an “ink” made from a mix of the new polymer and carbon nanotubes.  As their name implies, each of those tubes was only a few billionths of a meter in length. X-ray diffraction — an imaging tool that reveals the arrangement of individual molecules — shows that the polymers change from their messy non-crystal phase at warm temperatures to an orderly crystal phase when they’re cooler. This phase changes occur between 40º and 55º Celsius (104º and 131º Fahrenheit). Changing the polymer’s chemical recipe could allow it to change phases at different temperatures.
The new fabric performed well, Zhang says — better than his team had expected. Even after being folded 2,000 times, it worked as it was designed to do. But Granados-Focil at Clark University points out that the team never made a side-by-side comparison of the fabric’s durability with and without its phase-change component. He’d like to see such a comparison.
The Chinese team added nanotubes to the fabric to help it conduct electricity. Nanotubes also speed up the cloth’s ability to move heat around, Zhang explains. An added benefit, he notes: The tiny tubes add “radiation resistance.”
Here, Granados-Focil explains, “They’re talking about radio waves … Wi-Fi connections, that kind of radiation.” If used to encase a smartphone, he says, others “can’t access the information.” But that trait also confuses him. Considering the fabric’s electrical conductivity, he wonders: “In what scenario would you need to combine those two?”
“But being able to absorb all that radiation and not to seem hotter or colder than the environment around you,” he notes — “that could give you some camouflage property.” This attribute might add appeal for military or defense-type applications.
Byron Jones believes ordinary fashion designers would have little need or interest in such applications. A mechanical engineer, Jones works at Kansas State University in Manhattan. But years ago, he worked with companies that actually tried developing phase-change fabrics for everyday use. “My personal opinion,” he says, “is that phase-change materials in everyday clothing is more about marketing hype than it is about useful impact.”
Here’s the problem, Jones says. Your phase-change jacket absorbs heat as you get hot, then releases it as you cool off. You hope it will keep you comfortable. But it can’t absorb all your heat. Still, absorbing even 10 percent should keep you modestly comfy. And if you walk around for about 10 minutes in that jacket, 10 percent of the heat you give off over that time would come to about 72,000 joules. (Joule is a unit of energy.) For comparison, a regular light bulb emits about 60 joules per second.
According to the team’s data, each gram of their fabric absorbs 65 joules. Not 65 joules per second. It’s 65 joules once, during the phase-change. Afterwards, the polymer stops storing heat. So to absorb 72,000 joules, Jones explains, your jacket must have 1,100 grams — or 2.4 pounds — of the phase-change fabric. And that’s like carrying around two and a half cans of condensed soup. He concludes, “No matter how you hype it, you can’t get around these physics.” So it might work for a jacket, but hardly a tee-shirt.
Jones does see some possible uses, however. It might prove useful in a situation where you only need “a few minutes” of heating or cooling capacity. “Then you go back into an environment where the phase-change material is recharged” — returned to its heat-absorbing or heat-shedding state.
Granados-Focil agrees. “This electrical conductivity business — it’s interesting,” he says. For example, in gloves, it should mean you can operate touchscreens. And it might let you touch something really hot or cold for 30 seconds, without needing clunky gloves.
This technology “isn’t going to change all of our sweaters tomorrow,” Granados-Focil concludes. But for niche-type applications, he says “it could be interesting.

When someone pulls on a virtual reality headset, they’re ready to dive into a simulated world. They might be hanging out in VRChat or slashing beats in Beat Saber. Regardless, interacting with that world usually involves hand controllers. But new virtual reality — or VR — technology out of Australia is hands-free. Facial expressions allow users to interact with the virtual environment. This technology would allow people who can’t use handheld controllers to play virtual games.

This setup could make virtual worlds more accessible to people who can’t use their hands, says Arindam Dey. He studies human-computer interaction at the University of Queensland in Brisbane. Other hands-free VR tech has let people move through virtual worlds by using treadmills and eye-trackers. But not all people can walk on a treadmill. And most people find it a challenge to stare at one spot long enough for the VR system to register the action. Simply making faces may be an easier way for those who are disabled to navigate VR.
In the researchers’ new system, VR users wear a cap studded with sensors. Those sensors record brain activity. The sensors can also pick up facial movements that signal certain expressions. Facial data can then be used to control the user’s movement through a virtual world.

Facial expressions usually signal emotions. So Dey’s team designed three virtual environments for users to explore. An environment called “happy” required participants to catch butterflies with a virtual net. “Neutral” had them picking up items in a workshop. And in the “scary” one, they had to shoot zombies. These environments allowed the researchers to see whether situations designed to provoke certain emotions affected someone’s ability to control VR through expressions.
Eighteen young adults tested out the technology. Half of them learned to use three facial expressions to move through the virtual worlds. A smile walked them forward. A frown brought them to a stop. And to perform a task, they clenched their teeth. In the happy world, that task was swooping a net. In the neutral environment, it was picking up an item. In the scary world, it was shooting a zombie.
The other half of participants interacted with the virtual worlds using hand controllers. This was the control group. It allowed the researchers to compare use of facial expressions with the more common form of VR interaction.
Using facial expressions made participants feel more present inside the virtual worlds. But expressions were more challenging to use than hand controllers. Recordings from the sensor-laden cap showed that the brains of people using facial expressions were working harder than those who used hand controllers. But that could just be because these people were learning a new way to interact in VR. Perhaps the facial expression method would get easier with time. Importantly, virtual settings meant to trigger different emotions did not affect someone’s ability to control their VR using facial expressions.

History / Christopher Columbus
« on: March 13, 2022, 12:25:30 AM »
Christopher Columbus, Italian Cristoforo Colombo, Spanish Cristóbal Colón, (born between August 26 and October 31, 1451, Genoa [Italy]—died May 20, 1506, Valladolid, Spain), master navigator and admiral whose four transatlantic voyages (1492–93, 1493–96, 1498–1500, and 1502–04) opened the way for European exploration, exploitation, and colonization of the Americans. He has long been called the “discoverer” of the New World, although Vikings such as Leif Eriksson had visited North America five centuries earlier. Columbus made his transatlantic voyages under the sponsorship of Ferdinand II and Isabella I, the Catholic Monarchs of Aragon, Castile, and Leon in Spain. He was at first full of hope and ambition, an ambition partly gratified by his title “Admiral of the Ocean Sea,” awarded to him in April 1492, and by the grants enrolled in the Book of Privileges (a record of his titles and claims). However, he died a disappointed man.

History / History of timekeeping devices
« on: March 13, 2022, 12:04:40 AM »
The history of timekeeping devices dates back to when ancient civilizations first observed astronomical bodies as they moved across the sky. Devices and methods for keeping time have since then improved through a long series of new inventions and ideas. Sundials and water clocks originated from ancient Egypt, and were later used by the Babylonians, the Greeks and the Chinese; medieval Islamic water clocks were unrivalled in their sophistication until the mid-14th century. Incense clocks, which may have been invented in India, were being used in China by the 6th century. The hourglass, one of the few reliable methods of measuring time at sea, was a European invention and does not seem to have been used in China before the mid-16th century.

In medieval Europe, purely mechanical clocks were developed after the invention of the bell-striking alarm, used to warn a man to toll the monastic bell. The weight-driven mechanical clock, controlled by the action of a verge and foliot, was a synthesis of earlier ideas derived from European and Islamic science, and one of the most important inventions in the history of the timekeeping. The most famous mechanical clock was designed and built by Henry de Vic in c.1360—for the next 300 years, all the improvements in timekeeping were essentially developments based on it. The invention of the mainspring in the early 15th century allowed small clocks to be built for the first time.

From the 17th century, the discovery that clocks could be controlled by harmonic oscillators led to the most productive era in the history of timekeeping. Leonardo da Vinci had produced the earliest known drawings of a pendulum in 1493–1494, and in 1582 Galileo Galilei had investigated the regular swing of the pendulum, discovering that frequency was only dependent on length. The pendulum clock, designed and built by Dutch polymath Christiaan Huygens in 1656, was so much more accurate than other kinds of mechanical timekeepers that few clocks have survived with their verge and foliot mechanisms intact. Other innovations in timekeeping during this period include inventions for striking clocks, the repeating clock and the deadbeat escapement. Errors in early pendulum clocks were eclipsed by those caused by temperature variation, a problem tackled during the 18th century by the English clockmakers John Harrison and George Graham; only the invention of invar in 1895 eliminated the need for such innovations.

From the 18th century, a succession of innovations and inventions led to timekeeping devices becoming increasingly accurate. Following the Scilly naval disaster of 1707, after which governments offered a prize to anyone who could discover a way to determine longitude, Harrison built a succession of accurate timepieces. The electric clock, invented in 1840, was used to control the most accurate pendulum clocks until the 1940s, when quartz timers became the basis for the precise measurement of time and frequency. The wristwatch, which had been recognised as a valuable military tool during the Boer War, became a symbol of masculinity and bravado after World War I. During the 20th century the non-magnetic wristwatch, battery-driven watches, the quartz wristwatch, and transistors and plastic parts were all invented. The most accurate timekeeping devices in practical use today are atomic clocks, which can be accurate to within a few billionths of a second per year. They are used to calibrate other clocks and timekeeping instruments.

History / Soviet Union Collapse: The Nuclear Factor
« on: March 12, 2022, 11:55:16 PM »
Throughout the Cold War, the Soviet Union and the United States teetered on the edge of mutual nuclear destruction. What few had considered, however, was that the Soviet Union would be brought down by an incident involving a civilian nuclear plant. Gorbachev had been in power for just over a year when, on April 26, 1986, the Unit 4 reactor at the Chernobyl power station in Pryp’yat (now in Ukraine) exploded. The explosion and subsequent fires released more than 400 times the amount of radioactive fallout as the atomic bomb that was dropped on Hiroshima. The official response to the disaster would be a test of Gorbachev’s doctrine of openness, and, in that regard, glasnost would be found fatally wanting. Communist Party officials acted quickly to suppress information about the severity of the disaster, going as far as to order that May Day parades and celebrations in the affected area should proceed as planned despite the known risk of radiation exposure. Western reports about the dangerously high levels of wind-transported radioactivity were dismissed as gossip, while apparatchiks quietly collected Geiger counters from science classrooms. Workers were finally able to bring the radiation leak under control on May 4, but Gorbachev did not issue an official statement to the public until May 14, 18 days after the disaster. He characterized the incident at Chernobyl as a “misfortune” and pilloried Western media coverage as a “highly immoral campaign” of “malicious lies.” Over time, Communist Party propaganda was increasingly at odds with the daily experiences of those in the contamination zone who were dealing with the physical effects of radiation poisoning. Whatever trust remained in the Soviet system had been shattered. Decades later, Gorbachev marked the anniversary of the disaster by stating, “even more than my launch of perestroika, [Chernobyl] was perhaps the real cause of the collapse of the Soviet Union five years later.”

History / 5 Facts About the East India Company
« on: March 12, 2022, 11:50:33 PM »
The British East India Company was a private corporation formed in December 1600 to establish a British presence in the lucrative Indian spice trade, which until then had been monopolized by Spain and Portugal. The company eventually became an immensely powerful agent of British imperialism in South Asia and the de facto colonial ruler of large parts of India. Partly because of endemic corruption, the company was gradually deprived of its commercial monopoly and political control, and its Indian possessions were nationalized by the British crown in 1858. It was formally dissolved in 1874 by the East India Stock Dividend Redemption Act (1873).

1. In the 17th and 18th centuries, the East India Company relied on slave labor and trafficked in slaves from West and East Africa, especially Mozambique and Madagascar, transporting them to its holdings in India and Indonesia as well as to the island of St. Helena in the Atlantic Ocean. Although its slave traffic was small in comparison with transatlantic slave-trading enterprises such as the Royal African Company, the East India Company crucially relied on transfers of slaves with specialized skills and experience to manage its far-flung territories.

2. The East India Company controlled its own army, which by 1800 comprised some 200,000 soldiers, more than twice the membership of the British Army at that time. The company used its armed force to subdue Indian states and principalities with which it had initially entered into trading agreements, to enforce ruinous taxation, to carry out officially sanctioned looting, and to protect its economic exploitation of both skilled and unskilled Indian labor. The company’s army played a notorious role in the unsuccessful Indian Uprising (also called the Indian Mutiny) of 1857–58, in which Indian soldiers in the company’s employ led an armed revolt against their British officers that quickly gained popular support as a war for Indian independence. During more than a year of fighting, both sides committed atrocities, including massacres of civilians, though the company’s reprisals ultimately far outweighed the violence of the rebels. The rebellion brought about the effective abolishment of the East India Company in 1858.

3. Beginning in the early 19th century, the East India Company illegally sold opium to China to finance its purchases of Indian tea and other goods. Chinese opposition to that trade precipitated the First and Second Opium Wars (1839–42; 1856–60), in both of which British forces were victorious.

4. The company’s management was remarkably efficient and economical. During its first 20 years the East India Company was run from the home of its governor, Sir Thomas Smythe, and had a permanent staff of only six. In 1700 it operated with 35 permanent employees in its small London office. In 1785 it controlled a vast empire of millions of people with a permanent London staff of 159.

5. Following several years of misrule and a massive famine (1770) in Bengal, where the company had installed a puppet regime in 1757, the company’s land revenues fell precipitously, forcing it to appeal (1772) for an emergency loan of £1 million to avoid bankruptcy. Although the East India Company was bailed out by the British government, harsh criticism and investigations by parliamentary committees led to government oversight of its management (the Regulating Act of 1773) and later to government control of political policy in India (the India Act of 1784).

বায়ুদূষণের (Air Pollution) জেরে সুদূরপ্রসারী প্রভাব পড়েছে গোটা বিশ্বে। একই প্রভাব পড়ছে বাংলাদেশবাসীর জীবনেও। সমীক্ষা বলছে, সেই কারণে বাংলাদেশের (Bangladesh) মানুষের গড় আয়ু কমেছে প্রায় তিন বছর। নিকট প্রতিবেশী ভারত, মায়ানমার ও ভুটানের বায়ুদূষণের পরিস্থিতি বাংলাদেশের তুলনায় ভাল। ‘বিশ্বের বায়ু পরিস্থিতি-২০২০: বায়ুদূষণ কীভাবে বিশ্বজুড়ে মানুষের আয়ুর উপর প্রভাব ফেলছে’ নামের এক গবেষণায় উঠে এসেছে এই তথ্য। এই গবেষণাটি যৌথভাবে চালিয়েছে যুক্তরাষ্ট্রের হেলথ এফেক্টস ইনস্টিটিউট ও ইনস্টিটিউট ফর হেলথ মেট্রিক্স অ্যান্ড ইভ্যালুয়েশন। দক্ষিণ ও পূর্ব এশিয়ার দেশগুলোর মধ্যে বায়ুদূষণে সবচেয়ে বেশি গড় আয়ু কমেছে নেপালের মানুষের। গড় হিসাবে ৩.০৫ বছর।
বাংলাদেশ পরিসংখ্যান ব্যুরোর তথ্য অনুসারে, বর্তমানে দেশের মানুষের গড় আয়ু ৭২.৬ বছর। গোটা বিশ্বেই বায়ুদূষণের কারণে মানুষের গড় আয়ু কমেছে। গবেষণা প্রতিবেদনের তথ্য বলছে, বায়ুদূষণে বিশ্ববাসীর গড় আয়ু কমেছে এক বছর আট মাস। আরও জানা যাচ্ছে, বায়ুদূষণের কারণে মানুষের গড় আয়ু সবচেয়ে বেশি কমেছে দক্ষিণ এশিয়া, সাব সাহারা ও ওশেনিয়া অঞ্চলে। বিশ্ব স্বাস্থ্য সংস্থার (WHO) তথ্য বলছে, বায়ুদূষণে প্রতি বছর বিশ্বব্যাপী অন্তত ৭০ লক্ষ মানুষ প্রাণ হারান। বায়ুদূষণের কারণে চিনবাসীর গড় আয়ু কমেছে ১.৮৫ বছর।

Smartphone / Disadvantages of physical SIM cards
« on: March 10, 2022, 05:29:19 PM »
Physical SIM cards have been critical to the expansion of our present mobile network.
They do, however, have some drawbacks. Companies have reduced the size of SIM cards multiple times over the years, progressing from SIM to micro, and micro to nano. However, the outside plastic packaging that held the connections and chip was merely reduced as a result of these size reductions. The chip and contacts haven't shrunk in size in any way. In essence, SIM cards appear to be as compact as they possibly can be.
That is an uncomfortable possibility in an industry that is always looking for ways to shrink gadget footprints. While e-SIM devices have the potential to be very useful for mass-produced smartphones, they are not without problems. The transfer of credentials to a separate device is the first issue that must be addressed. SIM cards are not able to be easily copied or accessed remotely. This implies that if a user's phone breaks and they need to move their information to a smart smartphone, all they have to do is manually transfer the SIM card.
Another concern with e-SIM devices is that, while they provide privacy and the capacity to be programmed, they are actually attached to the phone and cannot be uninstalled. This could be a concern for those who don't want to be followed because phones with just an activated Sim are easily traced by the operator. It was formerly possible to eliminate a phone's SIM card and so stop it from connecting to a network, making it difficult to trace. As we know this is the first time Grameenphone offers e-SIM services in our country.

Smartphone / What is eSIM?
« on: March 10, 2022, 05:21:56 PM »
Recently, eSIMs have been making waves as the next step in mobile technology. Embedded-SIM, or eSIM, is a SIM card that can be electronically programmed into a mobile phone without the need for manual insertion. It works just like a regular SIM but does not require a physical card, and only works on devices with pre-installed eSIM support. Grameenphone has officially launched eSIM service in Bangladesh on 1 March 2022. Very few devices currently have eSIM support, and they need to be carrier-enabled for the eSIM to work.
Apple devices such as iPhone XR, iPhone 11 Pro, iPhone 12 and 13 have built-in eSIM support. Versions of Samsung Galaxy S20, S21, Note 20 and Galaxy Fold, as well as Google Pixel 3, 3a, 4, 4a, 5, 5a and 6 Pro also support eSIM.

Internet Technology / What is a fiber-optic network?
« on: March 10, 2022, 05:18:24 PM »
There are several different types of fiber-optic networks but they all begin with optic cables running from the network hub to the curb near your home or straight to your home to provide a fiber-optic internet connection. The fastest type of fiber network is called Fiber to the Home (FTTH) or Fiber to the Premises (FTTP) because it’s a 100% fiber-optic connection with optical fiber cables installed to terminals directly connected to houses, apartment buildings and businesses.
On the other hand, Fiber to the Curb (FTTC) is a partial fiber connection because the optical cables run to the curb near homes and businesses and copper cables carry the signals from the curb the rest of the way. Similarly, Fiber to the Building (FTTB) is when fiber cable goes to a point on a shared property and the other cabling provides the connection to offices or other spaces.

সুস্থ হয়ে বেঁচে থাকতে রোজ মাত্র ছয় হাজার পা ফেললেই হবে। তবে ‘একটু পা চালিয়ে ভাই’— হেলেদুলে পা ফেললে হবে না। হাঁটার জন্য ঘাম ঝরতে হবে অল্পবিস্তর। বিজ্ঞানীরা আগে হিসাব কষে দেখিয়েছিলেন, সুস্থ থাকতে হলে, বেশি দিন বাঁচতে হলে রোজ দিনভর যে কোনও সময় মিলিয়ে দশ হাজার পা ফেলতেই হবে। সাম্প্রতিক গবেষণা কিছুটা স্বস্তির খবর দিল। জানাল— দশ নয় ছয়। ছয় হাজার পা-ই যথেষ্ট বেশি দিন বাঁচতে চাইলে।গবেষণাপত্রটি প্রকাশিত হয়েছে আন্তর্জাতিক চিকিৎসাবিজ্ঞান গবেষণা পত্রিকা ‘দ্য ল্যান্সেট: পাবলিক হেল্থ’-এ।
এ ব্যাপারে আগে প্রকাশিত ১৫টি গবেষণার ফলাফল খতিয়ে দেখে এবং এশিয়া, ইউরোপ, অস্ট্রেলিয়া, উত্তর আমেরিকার মতো চারটি মহাদেশের কয়েক লক্ষ মানুষের উপর পরীক্ষা চালিয়ে গবেষকরা দেখেছেন বেশি দিন বেঁচে থাকতে চাইলে দিনে নিয়ম করে যে কোনও সময় মিলিয়ে কম করে মোট ছয় হাজার পা ফেললেই হবে। তবে একটু জোরে জোরে পা ফেলতে হবে। এই হিসাবে কিছুটা কম-বেশি হতেই পারে, কোন বয়সের মানুষ এই অভ্যাসে রপ্ত হচ্ছেন, শৈশব থেকে তাঁরা কী কী ধরনের রোগে বেশি দিন ভুগেছেন তার উপরেও অবশ্য।
তবে বেশি দিন বাঁচতে চাইলে যে রোজ নিয়ম করে ছয় হাজারের বেশি পা ফেলতেই হবে তা একেবারেই নয়, জানিয়েছেন আমেরিকার আমহার্স্টে ম্যাসাচুসেট্‌স বিশ্ববিদ্যালয়ের গবেষকরা। গবেষকরা জানিয়েছেন, মানুষ অনেক দীর্ঘ পথ পাড়ি দিতে পারে। যাকে বলা যায় ম্যারাথন দূরত্ব (ক্রীড়ায় যা ২৬ কিলোমিটার)। সেই ভাবেই মানুষের ক্রমবিবর্তন হয়েছে। খাদ্য ও জলের খোঁজে। সে সব জোগাড় করে প্রাণ বাঁচানোর তাগিদে। গবেষকদের অন্যতম ম্যাসাচুসেট্‌স বিশ্ববিদ্যালয়ের অধ্যাপক আমান্দা পালুচ বলেছেন, ‘‘এর জন্যই বিবর্তন আমাদের শরীরকে বদলে দিয়েছে। যেমন প্রয়োজন সেই মতো গড়ে তুলেছে। যাতে রোজ দীর্ঘ পথ হাঁটলে গা যতটা গরম হয়ে ওঠে, যতটা ঘাম ঝরে তাতে যেন মানবশরীরের বিপাকক্রিয়াগুলি স্বাভাবিকই থাকে। স্বাভাবিক থাকে হৃদযন্ত্র ও তার আশপাশের এলাকার কাজকর্ম। যেন স্বাভাবিকের মধ্যেই থাকে দেহে রক্তসংবহনের মাত্রা। রক্তকণিকাদের সংখ্যার অনুপাতও। সেই মতো তৈরি থাকে মানুষের হাড় ও পেশিগুলিও। এমনকি, মানসিক স্বাস্থ্যও।’’
তবে সবকিছুরই একটা সীমা থাকে। যা বয়সের সঙ্গে সঙ্গে স্বাভাবিক ভাবেই কমে। সেই সীমাটা রোজ দশ হাজার পা ফেললে হিতে বিপরীতও ডেকে আনতে পারে। বরং মেরেকেটে হাজার ছয়েক পা ফেললেই যথেষ্ট, জানিয়েছে গবেষণাপত্রটি। তা হলে আগের দশ হাজারি ধারণাটা কেন বদ্ধমূল হয়ে বসেছিল আমাদের মস্তিষ্কে? তারও ব্যাখ্যা দিয়েছেন আমান্দা। বলেছেন, ‘‘বেশি দিন বেঁচে থাকতে হলে কয়েক হাজার পা দিনে জোরে জোরে ফেলতেই হবে। এর অর্থ, একটু বেশি পরিশ্রম করতে হবে, এটাই বোঝানো। দশ হাজার বললে সেই পরিশ্রম কতটা তা বোঝানো যায়। যেমন কারও বিশালত্ব বোঝাতে দুম করে আমরা দশ গুণ বলে বসি!’’
গবেষকরা দেখেছেন, দিনে যাঁরা বেশি হাঁটাহাঁটি করেন এমন ৪০ বছর বয়সি বা তদোর্ধদের ২৫ শতাংশের অকালমৃত্যুর আশঙ্কা যাঁরা তা করেন না তাঁদের থেকে ৪৩/৫০ শতাংশ কম। আর বয়সটা যদি ৬০ বা তার কিছু বেশি হয় তা হলে দিনে নিয়ম করে ছয় হাজার পা জোরে জোরে ফেললেই হবে। এড়ানো সম্ভব হতে পারে অকালমৃত্যুর আশঙ্কা।তবে বয়স যাঁদের ৪০-এর নীচে, তাঁরা দিনে আট বা দশ হাজার পা ফেলতে পারেন জোরে জোরে। সে ক্ষেত্রে এই বাড়তি পরিশ্রম নেওয়ার ধকল তাঁদের শরীর সহ্য করতে পারবে। বাড়তি কোনও বিপদ ডেকে আনবে না। বরং এই পরিশ্রম হৃদযন্ত্র ও মস্তিষ্ককে আরও সচল সক্রিয় রাখতে সাহায্য করবে।

Geography / How big is our Earth?
« on: March 09, 2022, 02:00:09 AM »
Earth, the third planet from the sun, is the fifth-largest planet in the solar system; only the gas giants Jupiter, Saturn, Uranus and Neptune are bigger. Earth is the largest of the terrestrial planets of the inner solar system, bigger than Mercury, Venus and Mars.
The radius of Earth at the equator is 3,963 miles (6,378 kilometers), according to NASA's Goddard Space Flight Center in Greenbelt, Maryland. However, Earth is not quite a sphere. The planet's rotation causes it to bulge at the equator. Earth's polar radius is 3,950 miles (6,356 km) — a difference of 13 miles (22 km). Using those measurements, the equatorial circumference of Earth is about 24,901 miles (40,075 km). However, from pole to pole — the meridional circumference — Earth is only 24,860 miles (40,008 km) around. Our planet's shape, caused by the flattening at the poles, is called an oblate spheroid.
Those numbers make Earth just slightly bigger than Venus, whose equatorial radius is about 3,761 miles (6,052 km). Mars is much smaller than both Earth and Venus, with an equatorial radius of just 2,110 miles (3,396 km).But Earth and the other rocky planets are much smaller than the gas giants. For example, more than 1,300 Earths could fit inside Jupiter.
Earth's density is 5.513 grams per cubic centimeter, according to NASA. Earth is the densest planet in the solar system because of its metallic core and rocky mantle. Jupiter, which is 318 more massive than Earth, is less dense because it is made primarily of gases, such as hydrogen.
Earth's mass is 6.6 sextillion tons (5.9722 x 1024 kilograms). Its volume is about 260 billion cubic miles (1 trillion cubic kilometers).
The total surface area of Earth is about 197 million square miles (510 million square km). About 71% of our planet is covered by water and 29% by land. For comparison, the total surface area of Venus is roughly 178 million square miles (460 million square km) , and that of Mars is about 56 million square miles (144 million square km).
Mount Everest is the highest place on Earth above sea level, at 29,032 feet (8,849 meters), but it is not the highest point on Earth — that is, the place most distant from the center of the Earth. That distinction belongs to Mount Chimaborazo in the Andes Mountains in Ecuador, according to the U.S. National Oceanic and Atmospheric Administration (NOAA). Although Chimaborazo is about 10,000 feet (3,048 m) shorter (relative to sea level) than Everest, this mountain is about 6,800 feet (2,073 m) farther into space because of the equatorial bulge.
Everest and Chimborazo are nowhere near the tallest mountains in the solar system, however. The peak rising from Rheasilvia Crater on the asteroid Vesta, for example, is about 14 miles (22.5 km) tall. Mars' huge Olympus Mons volcano is nearly as high, at 13.6 miles (21.9 km), and it covers an area the size of the state of Arizona. The lowest point on Earth is Challenger Deep in the Mariana Trench in the western Pacific Ocean, according to NOAA. It reaches down about 36,200 feet (11,034 m) below sea level.

Science Discussion Forum / Global warming vs climate change
« on: March 09, 2022, 01:52:31 AM »
Many people use these two terms interchangeably, but we think it’s important to acknowledge their differences. Global warming is an increase in the Earth’s average surface temperature from human-made greenhouse gas emissions.

On the other hand, climate change refers to the long-term changes in the Earth’s climate, or a region on Earth, and includes more than just the average surface temperature. For example, variations in the amount of snow,  sea levels, and sea ice can all be consequences of climate change.

Science Discussion Forum / Artificial eyes
« on: March 09, 2022, 01:46:33 AM »
Bionic eyes have been a mainstay of science fiction for decades, but now real-world research is beginning to catch up with far-sighted storytellers. A raft of technologies is coming to market that restore sight to people with different kinds of vision impairment.
In January 2021, Israeli surgeons implanted the world’s first artificial cornea into a bilaterally blind, 78-year-old man. When his bandages were removed, the patient could read and recognise family members immediately. The implant also fuses naturally to human tissue without the recipient’s body rejecting it.
Likewise in 2020, Belgian scientists developed an artificial iris fitted to smart contact lenses that correct a number of vision disorders. And scientists are even working on wireless brain implants that bypass the eyes altogether.
Researchers at Montash University in Australia are working on trials for a system whereby users wear a pair of glasses fitted with a camera. This sends data directly to the implant, which sits on the surface of the brain and gives the user a rudimentary sense of sight.

Science Discussion Forum / Hydrogen planes
« on: March 09, 2022, 01:44:56 AM »
Carbon emissions are a huge concern when it comes to commercial flights, but there is a potential solution and it has received a lot of funding. A £15 million UK project has unveiled plans for a hydrogen-powered plane. This project is known as Fly Zero and is being led by the Aerospace Technology Institute in conjunction with the UK government.
The project has come up with a concept for a mid-size plane powered completely by liquid hydrogen. It would have the capacity to fly roughly 279 passengers halfway around the world without stopping. If this technology could be actualised, it could mean a zero-carbon flight with no stops between London and Western America or London to New Zealand with a single stop.

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