Lengthening the Life of LithiumIon Battery

Lengthening the Life of LithiumIon Battery Lengthening the Life of LithiumIon Battery An unprecedented increase in lithium-ion battery research has occurred in recent years, with the goals of improving performance, durability, and safetyespecially for electric-drive vehicles. To achieve these goals, afundamental understanding of the underlying degradation mechanisms that limit battery life is of critical importance. Research opportunities for mechanical engineers are plentiful and include material-structure relationships, thermal-electrochemical issues, and thermal management strategies.The lithium-ion battery is a dynamic system with multiple physicochemical interactions that occur at multiple scales, says Partha P. Mukherjee, assistant professor of mechanical engineering at Texas AM University. How can we optimize these fundamental interactions? What are the influences of electrochemistry and transport? How can we manipulate the interaction of nanomaterials and nanostructures at th e mesoscale to improve performance?Mechanical DegradationOne way to improve lithium-ion battery performance is by reducing or eliminating the degradation that occurs within the electrodes.Diffusion-induced stress and fracture formation in the active particles is a critical degradation issue in lithium-ion battery electrodes, says Mukherjee. We are trying to understand why these fractures form and the best ways to minimize this mechanical degradation. Lithium-ion battery pack for an electric vehicle. Image Wikimedia CommonsLithium-ion batteries work on the principle of lithium ions inserting and de-inserting into the host material latticea process known as intercalation. This intercalation of lithium ions into the material lattice structure causes volume expansion, which is known as diffusion-induced stress (DIS). For example, graphite, an anode material, shows 5-10% volume expansion, whereas high-capacity anode materials such as tin and silicon exhibit 200-350% volume expansion. Thi s diffusion-induced stress and volume expansion during lithium insertion, and the contraction during de-insertion, result in microfracture development. For high-volume expansion materials, this may lead to particle isolation and pulverization, reducing electrode life and overall performance.Fracture due to DIS of electrode active particles is one of the critical factors for capacity fade and impedance rise in lithium-ion batteries, says Mukherjee. The inherent stochastics underlying crack formation and propagation in brittle intercalation materials is critical toward understanding the degradation phenomena that limit battery life and performance.Controlling Fracture DevelopmentWhen the DIS stress exceeds the fracture threshold in existing structural flaws or cracks in the active particles, microfractures may develop in the particles. Orientation of the initial pre-existing flaw or crack can also impact how it will propagate over time. Fractures interfere with lithium transport and r educe performance. The fresh surfaces that result from these fractures can also induce the formation of solid electrolyte interphase layers, removing lithium from the transport mechanism and further reducing performance.Research to identify the impact of microscopic imperfections on the lithium-ion transport is still in its early stages.A key question to be answered is how to minimize the formation of cracks in electrode particles during operational conditions, without diminishing performance, says Mukherjee.To better understand this issue, Mukherjee and his research team developed a stochastic methodology for characterizing the diffusion-induced damage inside typical intercalation particles. The methodology is based on a random lattice spring model, coupled with solid-state diffusion of lithium in active particles and performance prediction analysis. A fracture phase-map was developed that shows the safe/unsafe operating regimes according to particle size and C-rate (charge/dischar ge rate).Higher C-rates can lead to a greater amount of micro-crack formation, which is also linked to the active particle size, says Mukherjee. For example, larger particles (10 micron radius) experience significant mechanical degradation at high C-rates, whereas smaller particles (0.5-1 micron) may exhibit only slight structural damage. Due to strain energy release, most of the damage occurs within the first two or three delithiation-lithiation cycles during subsequent cycles, damage propagation may not be significant.Future WorkBecause the majority of the mechanical degradation occurs during the first few cycles, there is potential for optimizing the influence of active particle morphology, size, mechano-electrochemical properties, and interactions with other components (such as binder, conductive additives) in the electrode microstructures. Smaller particles experience less stress during lithiation and delithiation. The presence of pre-existing cracks in particles also results i n strain energy release, which enhances mechanical and electrochemical stability. Based on this observation, it may be feasible to utilize specially designed imperfections in electrode materials to limit the growth of microfracturing.Understanding the underlying stochastics and mechano-electrochemical interactions related to diffusion-induced stress is an important step toward reducing mechanical degradation in lithium-ion battery electrodes, says Mukherjee. This has the potential to improve the performance and cycle life of lithium-ion batteries and broaden the scope of future electroactive materials design.Mark Crawford is an independent writer. For Further DiscussionA key question to be answered is how to minimize the formation of cracks in electrode particles during operational conditions, without diminishing performance.Partha P. Mukherjee, Texas A&M University

How to Craft a Better Accountant Cover Letter

How to Craft a Better Accountant Cover LetterHow to Craft a Better Accountant Cover LetterIn an age of LinkedIn, online job boards and applying for positions by smartphone, do accounting professionals still need to go that extra step and write a titelseite letter? Yes While it may not be as indispensable as it used to be, a well-written accountant titel letter still plays an important role in getting yur foot in the door.A good cover letter catches the attention of hiring managers and entices them to take a closer look at your accounting resume. Its also an opportunity for you to go beyond your skill set and make a personal case for how you can be of value to their organization.Whats mora, the letter offers a glimpse into your personality and shows initiative. After all, crafting an optional document takes work, and going the extra mile on your application demonstrates your eagerness to do more than just the minimum.Tips to perfect an accountant cover letterNow that weve established that including an accountant cover letter with your resume is a good idea, you should keep this advice in mind for how to write something impactful that will help you land an interviewShort is sweet. The barrage of information coming at all of us today has created attention spans that are shorter than ever before. The world of resumes is no exception. Online recruitment platforms mean hiring managers are often inundated with applications. So economy of words matters. Aim to write about three concise paragraphs instead of trying to rehash your resume. Keep it to one page, maximum. All a good cover letter needs to do is complement your accounting resume.Keep it mobile friendly. A hiring manager could peruse applications on any device. Make sure your accounting cover letter can be read easily, both on a smartphone and in print. To ensure your letter is mobile-friendly, keep the length at around 150 to 200 words so the reader wont have to scroll too much. If the job posting says you sho uld email your documents to the hiring manager, its a good idea to both paste it into the main body as well as send it as a PDF attachment.Make it unique. Ho-hum, generic cover letters wont make the sale for you. Write a new letter for each position. Start by customizing it with the company name and the specific opening youre applying for. Analyze the job posting to see which of your skills and experience to highlight, and find ways to show you can meet the employers specific needs. For example, if the posting emphasizes a comprehensive understanding of Statutory Accounting Principles (SAP), your letter should mention how youve used the ordnungsprinzip to develop high-level analyses to support decision-making processes.Show your personality. The best cover letters exhibit passion and ambition. Why do you want to work at this company? Why are you best suited for the role? How can you add value to the business? Put the answers in your own words.Check your work. Make sure whatever you write is correct, which indicates you are a stickler for detail and have done your research. Include your most impressive skills and experience from your resume. Also look for typos. Before you click send or apply, double- and triple-proof your cover letter, and consider having someone you know read through it, too.Include a call to action. The whole point of a cover letter is to engage prospective employers and encourage them to learn more about you. Close the letter by reiterating your enthusiasm for the position and requesting that they get in touch with you. End with a courteous sign-off and a thank you. Make sure your contact information is clear so the employer can reach you.Before you send the perfect cover letter, work with our recruiters to find your ideal job in accounting and finance.Things to avoid with your cover letterIn case you could use more tips or reminders, heres a list of donts as youre writing cover letters.Dont think of your accountant cover letter as an after thought. Its usually the first thing an employer will see.Dont write what looks like a canned letter. Personalize it.Dont use outdated contact information.Dont duplicate your resume in your accountant cover letter. This is an opportunity to make a connection and demonstrate your enthusiasm for the role.Dont be too wordy or lose focus.Dont point out the gaps in your skills or experience.Dont use poor grammar or miss any spelling errors.Dont use company jargon. Stick to terminology that is known and understood at an industry level.Dealing with online systemsOne more thing The vast majority of companies today use an applicant tracking system (ATS), either a job boards or their own. This means job seekers face multiple screens of questions and many fields to fill in, which can make the process frustrating, if not confusing. Here are some tips regarding what to do with your accounting cover letter onlineRead the instructions. Some tracking systems have text boxes for pasting in your cove r letter, while others want you to upload or email it. Follow the employers precise instructions, or your application may be rejected outright.Use the resume field. You often can upload more than one document. If you dont see a place for a cover letter, go ahead and add it after your resume.Look for leer text fields. Many tracking systems have fields that allow you to include additional information. Here is where your accountant cover letter can go if theres nowhere else for it.Email it directly. If the employers ATS doesnt allow you to upload or paste in a cover letter, do a little investigative work. Call the company and get the name and email of the person or persons reviewing applications, and email your letter directly.Highly skilled accountants may be in great demand, but they still have to make a good impression when applying for positions. When you take the time to craft a compelling cover letter for each job opening, you increase your chances that much more of making it to the next stage. Tags

The History of American Military Rank

The History of American Military RankThe History of American Military RankIn the U.S. Military services, rank determines who gets to tell whom what to do. The higher ones rank, the more authority, and responsibility they have. U.S. Military personnel fall into one of three categories Enlisted Members,Warrant OfficersCommissioned Officers Warrant officers outrank all enlisted members, and commissioned officers outrank all warrant officers and enlisted members. Rank and pay grade are closely associated terms, but not quite the saatkorn. Pay grade is an administrative classification, associated with a members pay. Rank is a title and denotes the members level of authority and responsibility. An E-1 is the lowest enlisted pay grade. That persons rank is a Private in the Army and Marine Corps, an Airman Basic in the Air Force, and a Seaman Recruit in the Navy and Coast Guard. Its also worth noting that in the Navy and Coast Guard, the term rank is not used among enlisted Sailors. The pro per term is rate. Through the ages, the badge of ranks has included such symbols as feathers, sashes, stripes, and showy uniforms. Even carrying different weapons has signified rank. The badges of rank have been worn on hats, shoulders, and around the waist and chest. Revolutionary War The American military adapted most of its rank insignia from the British. Before the Revolutionary War, Americans drilled with militia outfits based on the British tradition. Sailors followed the example of the most successful navy of the time the Royal Navy. So, the Continental Army had privates, sergeants, lieutenants, captains, colonels, generals, and several now-obsolete ranks like the coronet, subaltern, and ensign. One thing the Army didnt have welches enough money to buy uniforms.To solve this, Gen. George Washington wrote, As the Continental Army has, unfortunately, no uniforms, and consequently many inconveniences must arise from not being able to distinguish the commissioned officers fr om the privates, it is desired that some badge of distinction be immediately provided for instance that the field officers may have red or pink colored cockades in their hats, the captains yellow or buff, and the subalterns green. Even during the war, rank insignia evolved. In 1780, regulations prescribed two stars for major generals and one star for brigadiers worn on shoulder boards, or epaulets.The use of most English ranks carried on even after the United States won the war. The Army and Marine Corps used comparable ranks, especially after 1840. The Navy took a different route. Evolving Rank Structure The rank structure and insignia continued to evolve. Second lieutenants replaced the Armys coronets, ensigns, and subalterns, but they had no distinctive insignia until Congress gave them butterbars in 1917. Colonels received the eagle in 1832. From 1836, majors and lieutenant colonels were denoted by oak leave captains by double silver bars, or railroad tracks and first lieute nants, single silver bars. In the Navy, Captain was the highest rank until Congress created flag officers in 1857 before then, designating someone an admiral in the republic had been deemed too royal for the United States. Until 1857, the Navy had three grades of captain roughly equivalent to the Armys brigadier general, colonel and lieutenant colonel. Adding to the confusion, all Navy ship commanders are called captain, regardless of rank. Civil War With the onset of the Civil War, the highest grade captains became commodores and rear admirals and wore one-star and two-star epaulets, respectively. The lowest became commanders with oak leaves, while captains in the middle remained equal to Army colonels and wore eagles. At the same time, the Navy adopted a sleeve stripe system that became so complex that when David Glasgow Farragut became the services first full admiral in 1866, the stripes on his sleeves extended from cuff to elbow. The smaller sleeve stripes used today were i ntroduced in 1869. Chevrons Chevrons are V-shaped stripes whose use in the military go back to at least the 12th century. It was a badge of honor and used in heraldry. The British and French used chevrons- from the French word for roof- to signify thelength of service. Chevrons officially denoted rank in the U.S. military for the first time in 1817, when cadets at the U.S. Military Academy at West Point, N.Y., wore them on their sleeves. From West Point, chevrons spread to the Army and Marine Corps. The difference then was chevrons were worn points down until 1902when Army and Marine Corps enlisted personnel switched to the present points up configuration. Navy and Coast Guard petty officers trace their insignia heritage to the British. Petty officers were assistants to the officers aboard ship. The title wasnt a permanent rank and the men served at the captains pleasure. Petty officers lost their rank when the crew was paid off at the end of a voyage. New Ranks, New Insignia s In 1841, Navy petty officers received their first rank insignia- an eagle perched on an anchor. Ratings, or job skills, were incorporated into the insignia in 1866. In 1885, the Navy designated three classes of petty officers first, second and third. They added chevrons to designate the new ranks. The rank of chief petty officer was established in 1894. During World War II, the Army adopted technician grades. Technicians of a given grade earned the same pay and wore the same insignia as equivalent noncommissioned officers except for a small T centered under the chevrons. Technicians, despite the stripes, had no command authority over troops. This evolved into the specialist ranks, pay grades E-4 to E-7. The last vestige today survives plainly as specialist, pay grade E-4. When there were such people as specialists 7, they wore the current eagle symbol surmounted by three curved gold bars often called bird umbrellas. When the Air Force became a separate service in 1947, it kept the Army officer insignia and namesbut adopted different enlisted ranks and insignia. Warrant officers went through several iterations before the services arrived at todays configuration. The Navy had warrant officers from the start- they were specialists who saw to the care and running of the ship. The Army and Marines did not have warrants until the 20th century. Rank insignia for warrants last changed with the addition of chief warrant officer 5. The Air Force stopped appointing warrant officers in the 1950s and has none on active duty today. Other Rank Facts Ensigns started with the Army but ended with the Navy. The rank of Army ensign was long gone by the time the rank of Navy ensign was established in 1862. Ensigns received gold bars in 1922, some five years after equivalent Army second lieutenants received theirs.Lieutenant comes from the French lieu meaning place and tenant meaning holding. Lieutenants are placeholders. The British originally corrupted the French pronunc iation, pronouncing the word, lieuftenant, while Americans (probably because of French settler influence) maintained the original pronunciation. While majors outrank lieutenants, lieutenant generals outrankmajor generals. It comes from British tradition Generals were appointed for campaigns and often called captain generals. Their assistants were, naturally, lieutenant generals. At the same time, the chief administrative officer was the sergeant major general. Somewhere along the way, sergeant was dropped.Gold is worth more than silver, but silver outranks gold. It is because the Army decreed in 1832 that infantry colonels would wear gold eagles on an epaulet of silver and all other colonels would wear silver eagles on gold. When majors and lieutenant colonels received the leaves, this tradition could not continue. So silver leaves represented lieutenant colonels and gold, majors. The case of lieutenants is different First lieutenants had been wearing silver bars for 80 years before second lieutenants had any bars at all. Colonel is pronounced kernal because the British adopted the French spelling colonel but Spanish pronunciation coronel and then corrupted the pronunciation.While rank insignia is important, sometimes it isnt smart to wear them. When the rifled musket made its appearance in the Civil War, sharpshooters looked for officers. Officers soon learned to take off their rank insignia as they approached the battle line.The Air Force took a vote on their enlisted stripes. In 1948, then-Air Force Vice Chief of Staff Gen. Hoyt Vandenberg polled NCOs at Bolling Air Force Base in Washington, and 55 percent of them chose the basic design still used today. When the Air Force became a separate service in 1947, it kept the Army officer insignia and namesbut adopted different enlisted ranks and insignia.