Thursday, February 2, 2023

عملات البيتكوين


سلسلة ملكية مبسطة كما هو موضح في ورقة عمل البيتكوين البيضاء. [3] من الناحية العملية ، يمكن أن تحتوي المعاملة على أكثر من مُدخل واحد وأكثر من مُخرج. [45]

في blockchain ، يتم تسجيل عملات البيتكوين في عناوين البيتكوين. لا يتطلب إنشاء عنوان بيتكوين أكثر من اختيار مفتاح خاص صالح عشوائي وحساب عنوان البيتكوين المقابل. يمكن إجراء هذا الحساب في جزء من الثانية. لكن العكس ، حساب المفتاح الخاص لعنوان بيتكوين معين ، غير ممكن عمليًا. [7] : الفصل. 4 يمكن للمستخدمين إخبار الآخرين أو جعل عنوان Bitcoin عامًا دون المساس بمفتاحه الخاص المقابل. علاوة على ذلك ، فإن عدد المفاتيح الخاصة الصالحة كبير جدًا لدرجة أنه من غير المحتمل للغاية أن يقوم شخص ما بحساب زوج مفاتيح قيد الاستخدام بالفعل ولديه أموال. العدد الهائل من المفاتيح الخاصة الصالحة يجعل من غير المجدي استخدام القوة الغاشمة للتلاعب بمفتاح خاص. لتتمكن من إنفاق عملات البيتكوين الخاصة به ، يجب على المالك معرفة المفتاح الخاص المقابل والتوقيع رقميًا على المعاملة. [د] تتحقق الشبكة من التوقيع باستخدام المفتاح العام ؛ لا يتم الكشف عن المفتاح الخاص أبدًا. [7] : الفصل. 5 

في حالة فقدان المفتاح الخاص ، لن تتعرف شبكة البيتكوين على أي دليل آخر على الملكية ؛ [42] تصبح العملات المعدنية غير صالحة للاستعمال ، وتُفقد فعليًا. على سبيل المثال ، في عام 2013 ، ادعى أحد المستخدمين أنه فقد 7500 ين ، بقيمة 7.5 مليون دولار في ذلك الوقت ، عندما قام بطريق الخطأ بتجاهل محرك أقراص ثابت يحتوي على مفتاحه الخاص. [49] يُعتقد أن حوالي 20٪ من جميع عملات البيتكوين قد فقدت - كان من الممكن أن تبلغ قيمتها السوقية حوالي 20 مليار دولار بأسعار يوليو 2018. [50]

لضمان أمان عملات البيتكوين ، يجب الحفاظ على سرية المفتاح الخاص. [7] : الفصل. 10  إذا تم الكشف عن المفتاح الخاص لطرف ثالث ، على سبيل المثال من خلال خرق البيانات ، يمكن للطرف الثالث استخدامه لسرقة أي عملات البيتكوين المرتبطة به . [٥١] اعتبارًا من ديسمبر 2017 ، سُرق حوالي 980.000 ين من بورصات العملات المشفرة . [52]

فيما يتعلق بتوزيع الملكية ، اعتبارًا من 28 ديسمبر 2022 ، تمتلك 9.62٪ من عناوين البيتكوين 98.51٪ من جميع عملات البيتكوين التي تم تعدينها على الإطلاق. [53] يُعتقد أن أكبر هذه العناوين تنتمي إلى البورصات ، والتي تحتفظ بعملة البيتكوين الخاصة بها في التخزين البارد. [54]

التعدين

انظر أيضًا: شبكة البيتكوين § التعدين
استخدم عمال مناجم البيتكوين الأوائل وحدات معالجة الرسومات ( GPU) للتعدين ، حيث كانت أكثر ملاءمة لخوارزمية إثبات العمل من وحدات المعالجة المركزية ( CPU ) . [55]
قام الهواة في وقت لاحق بتعدين عملات البيتكوين باستخدام رقائق FPGA و ASIC المتخصصة . أصبحت الرقائق المصورة قديمة بسبب الصعوبة المتزايدة.
اليوم ، تخصص شركات تعدين البيتكوين مرافق لإسكان وتشغيل كميات كبيرة من أجهزة التعدين عالية الأداء. [56]
مخطط شبه لوغاريتمي لصعوبة التعدين النسبية [هـ] [40]

التعدين هو خدمة لحفظ السجلات تتم من خلال استخدام قوة معالجة الكمبيوتر . [و] يحافظ المعدنون على blockchain متسقًا وكاملًا وغير قابل للتغيير من خلال تجميع معاملات البث الجديدة بشكل متكرر في كتلة ، والتي يتم بثها بعد ذلك إلى الشبكة والتحقق منها بواسطة عقد المستلم. [41] تحتوي كل كتلة على تجزئة تشفير SHA-256 للكتلة السابقة ، [41] وبالتالي ربطها بالكتلة السابقة وإعطاء blockchain اسمها. [7] : الفصل. 7  [41]

لكي يتم قبولها من قبل بقية الشبكة ، يجب أن تحتوي الكتلة الجديدة على إثبات العمل (PoW). [41] [g] يتطلب PoW من عمال المناجم العثور على رقم يسمى nonce (رقم مستخدم مرة واحدة فقط) ، بحيث عندما يتم تجزئة محتوى الكتلة مع nonce ، تكون النتيجة أصغر عدديًا من هدف صعوبة الشبكة . [7] : الفصل. 8 من السهل على أي عقدة في الشبكة التحقق من إثبات العمل هذا ، ولكن إنشاءه يستغرق وقتًا طويلاً للغاية. يجب على المعدنين تجربة العديد من قيم nonce المختلفة (عادةً ما يكون تسلسل القيم المختبرة هو الأرقام الطبيعية التصاعدية: 0 ، 1 ، 2 ، 3 ، ...) قبل أن تكون النتيجة أقل من هدف الصعوبة. نظرًا لأن هدف الصعوبة صغير جدًا مقارنة بتجزئة SHA-256 النموذجية ، فإن تجزئة الكتلة تحتوي على العديد من الأصفار البادئة [7] : ch. 8  كما يمكن رؤيته في مثال تجزئة الكتلة هذا:

0000000000000000000590fc0f3eba193a278534220b2b37e9849e1a770ca959

من خلال تعديل هدف الصعوبة هذا ، يمكن تغيير مقدار العمل المطلوب لإنشاء كتلة. كل 2016 كتلة (حوالي 14 يومًا مع إعطاء 10 دقائق تقريبًا لكل كتلة) ، تضبط العقد بشكل حاسم هدف الصعوبة بناءً على المعدل الأخير لتوليد الكتلة ، بهدف الحفاظ على متوسط الوقت بين الكتل الجديدة في عشر دقائق. وبهذه الطريقة يتكيف النظام تلقائيًا مع إجمالي كمية طاقة التعدين على الشبكة. [7] : الفصل. 8  اعتبارًا من أبريل 2022 ، يتطلب الأمر في المتوسط 122 sextillion (122 ألف مليار مليار) محاولة لإنشاء تجزئة كتلة أصغر من هدف الصعوبة. [59] الحسابات بهذا الحجم باهظة الثمن وتستخدم أجهزة متخصصة. [60]

يجعل نظام إثبات العمل ، جنبًا إلى جنب مع تسلسل الكتل ، التعديلات على blockchain صعبة للغاية ، حيث يجب على المهاجم تعديل جميع الكتل اللاحقة من أجل قبول تعديلات كتلة واحدة. [61] مع إنشاء كتل جديدة بشكل مستمر ، تزداد صعوبة تعديل كتلة قديمة مع مرور الوقت ويزداد عدد الكتل اللاحقة (وتسمى أيضًا تأكيدات الكتلة المعينة). [41]

يتم تجميع الغالبية العظمى من طاقة التعدين معًا في مجمعات التعدين لتقليل التباين في دخل عمال المناجم. قد يضطر عمال المناجم المستقلون إلى العمل لعدة سنوات لتعدين كتلة واحدة من المعاملات وتلقي الدفع. في تجمع التعدين ، يتقاضى جميع عمال المناجم المشاركين رواتبهم في كل مرة يقوم فيها أي مشارك بإنشاء كتلة. يتناسب هذا المبلغ مع حجم العمل الذي ساهم به عامل منجم فردي في المجمع. [62] [ مطلوب مصدر أفضل ]

يتبرع

إجمالي عملات البيتكوين المتداولة [40]

كل 10 دقائق ، [63] يسمح للعامل الناجح في العثور على الكتلة الجديدة من قبل بقية الشبكة بتحصيل جميع رسوم المعاملات لأنفسهم من المعاملات التي تم تضمينها في الكتلة ، بالإضافة إلى مكافأة محددة مسبقًا من عملات البيتكوين التي تم إنشاؤها حديثًا. [٦٤] اعتبارًا من 11 مايو 2020 ، تبلغ هذه المكافأة حاليًا 6.25 في عملات البيتكوين المنشأة حديثًا لكل كتلة. [65] للمطالبة بهذه المكافأة ، يتم تضمين معاملة خاصة تسمى coinbase في الكتلة ، مع عامل المنجم باعتباره المستفيد. [7] : الفصل. 8  تم إنشاء جميع عملات البيتكوين الموجودة من خلال هذا النوع من المعاملات. بروتوكول البيتكوينيحدد أن مكافأة إضافة كتلة سيتم تخفيضها بمقدار النصف كل 210.000 كتلة (كل أربع سنوات تقريبًا). لذلك من خلال النظر في النصف كل 210.000 كتلة ومتوسط وقت إنشاء الكتلة لمدة 10 دقائق ، يمكن للمرء أن يحسب أنه سيتم الوصول إلى الحد الأقصى البالغ 21 مليون [h] تقريبًا في 5 أكتوبر 2138. [66] بعد ذلك ، سيتم مكافأة عامل التعدين الناجح برسوم المعاملات فقط. [67]

اللامركزية

عملة البيتكوين لامركزية على هذا النحو: [5]

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the bitcoin system

Units and divisibility

The unit of account of the bitcoin system is the bitcoin. Currency codes for representing bitcoin are BTC[a] and XBT.[b][37]: 2  Its Unicode character is ₿.[1] One bitcoin is divisible to eight decimal places.[7]: ch. 5  Units for smaller amounts of bitcoin are the millibitcoin (mBTC), equal to 1⁄1000 bitcoin, and the satoshi (sat), which is the smallest possible division, and named in homage to bitcoin's creator, representing 1⁄100000000 (one hundred millionth) bitcoin.[2] 100,000 satoshis are one mBTC.[38]

Blockchain

Data structure of blocks in the ledger
Number of bitcoin transactions per month, semilogarithmic plot[39]
Number of unspent transaction outputs[40]

The bitcoin blockchain is a public ledger that records bitcoin transactions.[41] It is implemented as a chain of blocks, each block containing a cryptographic hash of the previous block up to the genesis block[c] in the chain. A network of communicating nodes running bitcoin software maintains the blockchain.[42]: 215–219  Transactions of the form payer X sends Y bitcoins to payee Z are broadcast to this network using readily available software applications.

Network nodes can validate transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other nodes. To achieve independent verification of the chain of ownership, each network node stores its own copy of the blockchain.[43] At varying intervals of time averaging to every 10 minutes, a new group of accepted transactions, called a block, is created, added to the blockchain, and quickly published to all nodes, without requiring central oversight. This allows bitcoin software to determine when a particular bitcoin was spent, which is needed to prevent double-spending. A conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, but as a digital ledger, bitcoins only exist by virtue of the blockchain; they are represented by the unspent outputs of transactions.[7]: ch. 5 

Individual blocks, public addresses, and transactions within blocks can be examined using a blockchain explorer.[44]

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Bitcoin

Bitcoin (abbreviation: BTC[a] or XBT[b]; sign: ₿) is a protocol which implements a highly available, public, and decentralized ledger. In order to update the ledger, a user must prove they control an entry in the ledger. The protocol specifies that the entry indicates an amount of a token, bitcoin with a minuscule b. The user can update the ledger, assigning some of their bitcoin to another entry in the ledger. Because the token has characteristics of money, it can be thought of as a digital currency.[10]

Bitcoin transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. The cryptocurrency was invented in 2008 by an unknown person or group of people using the name Satoshi Nakamoto.[11] The currency began use in 2009,[12] when its implementation was released as open-source software.[7]: ch. 1  The word "bitcoin" was defined in a white paper published on October 31, 2008.[3][13] It is a compound of the words bit and coin.[14]

Bitcoin is legal in seven of the top ten world economies by GDP in 2022.[15][16] The Library of Congress reports that, as of November 2021, nine countries have fully banned bitcoin use, while a further forty-two have implicitly banned it.[17] A few governments have used bitcoin in some capacity. El Salvador has adopted Bitcoin as legal tender, although use by merchants remains low. Ukraine has accepted cryptocurrency donations to fund the resistance to the 2022 Russian invasion. Iran has used bitcoin to bypass sanctions. In the United States, there is "no intention" to ban Bitcoin.[18]

Bitcoin has been described as an economic bubble by at least eight recipients of the Nobel Memorial Prize in Economic Sciences.[19]

The environmental impact of bitcoin is worth noting.[20] Its proof-of-work algorithm for bitcoin mining is designed to be computationally difficult, which requires the consumption of increasing quantities of electricity, the generation of which has contributed to climate change.[21][22] According to the University of Cambridge, bitcoin has emitted an estimated 200 million metric tonnes of carbon dioxide since its launch, [23] or about 0.04% of all carbon dioxide released since 2009.[24]

Bitcoin miners have an economic incentive to use the cheapest forms of energy.[25][26] Renewable energy is the cheapest form of energy over time,[27] so it is in a Bitcoin miner's economic interest to use the cheaper renewable energy when possible.[28] For instance, the UNESCO World Heritage Site, Virunga National Park, in eastern Congo, Africa pays for its operations, using a profitable Bitcoin mining operation powered by the Park's hydroelectric plant.[29] Oil and gas giant Exxon mines Bitcoin using the natural gas flared by oil mining operations to generate their electricity.[30] Mining Bitcoin this way makes use of an otherwise "monumental waste of a valuable natural resource".[31] Still other miners reduce their overall energy bill by using the heat generated by their computers to heat their homes,[32] or hot tubs.[33]

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Wednesday, January 25, 2023

Teacher Builds Better Balance for Fun in Retirement

Many people think of retirement as a period in life full of baking cookies, swinging on the porch, and golfing. But for many retirees, that routine might sound like a nice vacation for a little while but becomes tedious on a daily basis.

Karen J. was one of those retirees. She didn't want to settle quietly into her hobbies after she retired from teaching. The desire to fill up some of her time and satisfy her quest for continual learning took her back to the classroom part-time.

However, it didn't take long for her to realize a traditional teaching role in a classroom was no longer an ideal fit for her retirement years. "Being inside the school working with a very limited and tight schedule, I decided I wanted more flexibility," Karen says.

Seeking a Better Work-Life Balance in Retirement

Karen also needed a job that provided more consistent income to add to her savings and boost her hobby fund. "Not getting a salary when schools are closed, on holidays, during vacation weeks, or over the entire summer was a bit stressful!"

But Karen found that it was challenging to find a part-time job that matched her professional skills and experience on her own, which led her to FlexJobs.

Discovering New Options

Through FlexJobs, Karen was able to land not one but two part-time, flexible positions with TutorMe and Littera Education. And together, they fit her needs perfectly. Now, Karen is busy "enjoying more of life by having time for other pursuits, piano, crafts, church activities, or simply being with friends."

"I enjoy being at home because it is quiet. I can take breaks when needed, schedule work, and not feel rushed to get from one place to another by a certain time. Now, I can leave for appointments or just have additional time for my hobbies."

Beyond balancing her time, Karen enjoys staying relevant and learning new skills that align with her lifelong career. "These roles give me additional training since I am a lifelong learner and still would like to help students achieve success."

Advice to Anyone Considering a FlexJobs Membership

Like many retirees, Karen noted that it's a balancing act to fight against age bias and other stereotypes about retirees. She suggests that other retirees update their resumes strategically with a focus on communicating both their experience and desire to keep working.

And even though budgets can be tight in retirement, Karen thinks the paid membership is well worth it. She says, "Try it for three months and keep looking! FlexJobs has a LOT of jobs."

Create Your Own Retirement Rules

There is no standard blueprint for retirement anymore. As Karen discovered, you can create your work-life balance rules.

If you're ready to explore your flexible work options, FlexJobs can help. We post jobs daily in over 50 career categories, and we have an entire team of real people dedicated to verifying those jobs to ensure that our members only see legitimate opportunities. Take the tour and discover all of the ways FlexJobs can support you!

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Balance and a Rewarding Career Using FlexJobs

For many, the United States Census Bureau study about commuting comes as no surprise. The Bureau's report shares that the average time spent commuting back and forth to work has grown to almost 30 minutes each way. And for most professionals who work in an office setting, giving up five hours of life each week for a commute is pretty standard.

But Sara S. struggled with a lengthy commute combined with long, draining hours. She realized that something had to change. Her work life was taking a toll on her family and personal commitments and pushing her to professional burnout. It was time to take back control of her life.

Committing to Pursuing Balance

Recognizing that she needed a change, Sara looked for remote roles independently. It was only a short time before she realized she was spending more time sourcing legitimate positions than she was applying for and following up on them.

"I had been looking for a remote position for a few months and wasted so much time and energy on fake job leads." Even with the many awareness campaigns, job seekers like Sara are often overwhelmed with the number of scams targeting job seekers. Fortunately, she found FlexJobs, and her job search became streamlined and productive.

Building a Rewarding Career

Sara knew that her next role needed to do more than create balance. She was also determined that it would be a quality position aligned with her career goals. "I didn't want to step backward in my career or be stuck in a position with no growth opportunities."

Fortunately, Sara remained focused on her goals and found a perfect fit in a fully remote role with UnitedHealth Group. Now, Sara can be more present for her family without having to put her career to the side. "I found an organization I can grow with, professionally and personally."

Thriving Throughout All Areas

If you ask Sara how working remotely has affected her life, she'll tell you she's enjoying building better balance in the larger, more apparent areas of her life. "I have more time for the things that are important to me—my kids, my education goals, and my health," she says.

But like most professionals new to remote work, Sara discovered that work flexibility has also enhanced her life in other areas. "I am saving on gas and auto expenses, eating healthier, and I can wear activewear to work, so I go for a jog or do Pilates on my breaks!"

Advocating for Work Flexibility

Now that Sara is thriving in a meaningful role supporting her work-life balance, she has become an advocate for others to make effective changes in their lives. "I have recommended FlexJobs to so many people. It was well worth purchasing the membership."

Her guidance to others looking for more work freedom? Your job search is much more than tailoring a resume and hitting "submit." Sara says, "Don't forget about the value of networking," also stating that, "A flawless resume is useless if no one ever reads it."

Create Your Own Success Story

We hear from job seekers like Sara every day, sharing the enormous impact that flexible work has made on their lives.

If you're ready to build a better work-life balance, take the tour and discover all of the resources that FlexJobs offers to support you in your job search.

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Tuesday, January 24, 2023

Why we don’t set the og:image:alt tag

 Users often ask us why we don’t include a og:image:alt tag in the SEO and social tags that we add to pages. Alt attributes are good for accessibility, so sharing them with Facebook must be a good thing, right? Well, it turns out that it’s not that simple! We actually removed support for the og:image:alt tag in 2019, because we think that it can harm accessibility. Read on to find out why.

Challenges with alt attributes

Alternative text is important for accessibility and to help search engines find out what your content is about. Read more about the importance of the image alternative text. You may also want to learn how to optimize your alternative text for better accessibility and SEO.

Contrary to popular understanding, the alternative text should not describe the image. Rather, it should describe the image’s purpose, which varies depending on usage and context.

The World Wide Web Consortium (W3C) distinguish a few different types of image purpose: Informative images, Functional images, Decorative images, etc. They also provide an Alt decision tree for some quick help on deciding which category a particular image fits into. As a good rule of thumb: Images that are purely decorative don’t need an alternative text. Informative and functional images do.

One image, many alternative texts

The root problem with WordPress (and most similar systems) is that it only allows you to set a single default alternative text. Images often need many different alternative texts, depending on their purpose and context. Luckily, it’s possible to micro-manage the alternative text and change it in the post content, as the default one won’t fit all the use cases. Let’s go through a few examples to better understand this limitation.

We upload the following image to the WordPress media library. The image represents some pizza with pepperoni (note: it’s the Italian version of Pizza with pepperoni):

Pizza with pepperoni

We set the image alternative text to:

Pizza with pepperoni

The alternative text describes the image, right? We’re all set up then! Wait a moment: Would that alternative text be a good one though? In most cases, the answer is: No. We didn’t take into consideration the actual usage of the image and its context.

Decorative purpose

Let’s say we’re going to use our Pizza image in a post where the image doesn’t add any meaningful information or function to the post content. The image is purely decorative. In this case, we should change the default alt attribute in the post content and make it empty:

<img src="image.png" alt="">
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How we built the inclusive language analysis in Yoast SEO

 Yoast SEO now comes with a new analysis to make your content even more accessible to all: the inclusive language analysis. This analysis helps you write more inclusively, lowering the likelihood that you’ll exclude someone from your content. That means you can reach a wider audience. But how does this analysis work? And how was »

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Yoast SEO Schema tab helps you set your structured data

 Using the Yoast SEO structured data content blocks, the correct Schema will automatically be added by the plugin. Also, Yoast SEO uses sensible default to describe your pages. If you need something more specific, you can change the content type for specific posts or pages in the Schema tab — you can find this in the meta box or the block editor sidebar. Here, you can describe your Contact page as being a ContactPage so search engines can understand. Find out more about selecting the Page or Article type in your Schema settings.

Use the Schema tab in Yoast SEO to specify different content types

FAQ structured data is so cool

Structured data is hot. It is one of the foundations of the web today and its importance will only increase with time. In this post, I’ve shown you one of the newest Schema additions, and you’ll increasingly see this pop up in the search results.

For more information on our Schema structured data implementation, please read our Schema documentation.

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Wednesday, March 31, 2021

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Persian kittens for sale

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