The history of women in engineering is a long and rich narrative, filled with individuals who stood out for their accomplishments and innovations. From prior to the acceptance of women into academic institutions, when a number of women pursued engineering studies privately, through the 20th century when women broke down academic and professional barriers, the contributions of women to the Civil Engineering profession cannot be overstated.

Each of the engineers below has had an impact on the profession, and has helped pave the way for future generations of engineers to have more opportunities for success.

منبع : سایت انجمن مهندسین عمران آمریکا 

Inspired by a toy, the ‘buckliball’ — a collapsible structure fabricated from a single piece of material — represents a new class of 3-D, origami-like structures

Motivated by the desire to determine the simplest 3-D structure that could take advantage of mechanical instability to collapse reversibly, a group of engineers at MIT and Harvard University were stymied — until one of them happened across a collapsible, spherical toy that resembled the structures they’d been exploring, but with a complex layout of 26 solid moving elements and 48 rotating hinges.

The toy inspired the engineers to create the “buckliball,” a hollow, spherical object made of soft rubber containing no moving parts, but fashioned with 24 carefully spaced dimples. When the air is sucked out of a buckliball with a syringe, the thin ligaments forming columns between lateral dimples collapse. This is the engineering equivalent of applying equal load on all beams in a structure simultaneously to induce buckling, a phenomenon first studied by mathematician Leonhard Euler in 1757.

When the buckliball’s thin ligaments buckle, the thicker ligaments forming rows between dimples undergo a series of movements the researchers refer to as a “cooperative buckling cascade.” Some of the thick ligaments rotate clockwise, others counterclockwise — but all move simultaneously and harmoniously, turning the original circular dimples into vertical and horizontal ellipses in alternating patterns before closing them entirely. As a result, the buckliball morphs into a rhombicuboctahedron about half the size (46 percent) of the original sphere.

The researchers named their new structure for its use of buckling and its resemblance to buckyballs, spherical all-carbon molecules whose name was inspired by the geodesic domes created by architect-inventor Buckminster Fuller. The buckliball is the first morphable structure to incorporate buckling as a desirable engineering design element. The buckling process induces folding in portions of the sphere — similar to the way paper folds in origami — so the researchers place their buckliball in a larger framework of buckling-induced origami they call “buckligami.”

Because their collapse is fully reversible and can be achieved without moving parts, morphable structures such as the buckliball have the potential for widespread applications, from the micro- to macroscale. They could be used to create large buildings with collapsible roofs or walls, tiny drug-delivery capsules or soft movable joints requiring no mechanical pieces. They also have the potential to transform Transformers and other kinds of toys. (The toy that provided the researchers’ epiphany is the Hoberman Twist-O.)

The Buckliball
Video: Lucy Lindsey/Melanie Gonick; footage courtesy of Jongmin Shim, Katia Bertoldi and Pedro Reis

The researchers — Jongmin Shim MS ’05, PhD ’10, a postdoc at Harvard; Claude Perdigo, a visiting graduate student at MIT; Elizabeth Chen, a recent graduate of the University of Michigan who will join Harvard as a postdoc in the fall; Katia Bertoldi, an assistant professor in applied mechanics at Harvard; and Pedro Reis, the Esther and Harold E. Edgerton Assistant Professor of Civil and Environmental Engineering and Mechanical Engineering at MIT — wrote a paper about this work that appears this week in the Proceedings of the National Academy of Sciences.

“In civil engineering, buckling is commonly associated with failure that must be avoided. For example, one typically wants to calculate the buckling criterion for columns and apply an additional safety factor, to ensure that a building stands,” Reis says. “We are trying to change this paradigm by turning failure into functionality in soft mechanical structures. For us, the buckliball is the first such object, but there will be many others.” For instance, a robotic arm could be built from a single piece of material using a precisely engineered pattern of dimples at the intended hinging points that, when activated by a pressure signal, would bend.

“The buckliball not only opens avenues for the design of foldable structures over a wide range of length scales, but may also be used as a building block for creating new materials with unusual properties, capable of dramatic contraction in all directions,” Bertoldi says.

Reis’s research uses precision tabletop-scale lab tests and mathematical analysis to determine the basic physics underlying the mechanical behavior of materials. Bertoldi’s research group uses tools from continuum and computational mechanics to unravel the mechanics of soft structures. The two teams collaborated on the buckliball: Reis’ team performed the lab experiments with the help of digital fabrication techniques (such as 3-D printing) to create objects with precise geometry, and Bertoldi’s group used computation to further analyze the detailed mechanics of the process.

Chen, who was visiting Harvard at the time, determined that only five spherical geometric structures have the potential for reversible buckling-induced collapse. (The specific example of Fuller’s 12-hole rhombicuboctahedron that collapses into a cuboctahedron is one of these five.) Design parameters for buckliballs include dimple size, the thickness of the thin shell inside the dimple and the stiffness of the material used to fabricate the buckliball.

Nature, it appears, has already figured this out. Viruses inject their nucleic acids into a host through a reversible structural transformation in which 60 holes open or close based on changes in the acidity of the cell’s environment, a different mechanism that achieves a similar reversible collapse at the nanoscale.

“What’s exciting about this work is that it uses instabilities to basically amplify small or moderate pressures into dramatic motion,” says Carmel Majidi, an assistant professor of mechanical engineering at Carnegie Mellon University whose research in soft robotics focuses on stretchable skin-like materials containing sensors. “One limitation of working with soft-material robotics is that they’re soft; they can’t produce the high pressures you get with heavy machines, so you’re left with machines that provide only fairly moderate pressures. This makes it difficult to achieve dramatic deformations. If you use a robotic skin as an assistive medical device on a human, it can monitor motion. But with advancements like the buckliball, the skin may even be able to actively change its shape and directly help with motor tasks.”

The work was funded through a National Science Foundation grant to the Harvard Materials Research Science and Engineering Center and by funds from Harvard University and MIT.

منبع : MIT NEWS

آوریل 2012

تعداد صفحات : 137 | انگلیسی | پی دی اف | 32 مگابایت

نامیدن هر سال به نام یک حیوان، بیشتر در اثر عوامل اعتقادی یا فرهنگی در تقویم بعضی از ملل مرسوم شده است. این نوع عوامل از ریشه هایی سرچشمه می گیرد که با تقویم این گونه ملل در ارتباط است.

تقویم ترکی – مغولی، از حدود قرن هفتم هجری قمری یعنی پس از استیلای مغول بر ایران، به تقویم ایرانیان راه یافت. این تقویم از نوع شمسی – قمری است، بدین معنی که سال آن و ماه های آن قمری است. اسامی 12 ماه قمری این تقویم در ترکی به ترتیب به معنی : ماه اول، ماه دوم و... نامیده می شود. این تقویم دارای دوره 12 ساله حیوانی است که اسامی معادل فارسی سالهای آن، به ترتیب عبارتند از : موش ، گاو، پلنگ، خرگوش، نهنگ، مار، اسب، گوسفند، میمون، مرغ ، سگ و خوک.
در ایران، استفاده از این تقویم در دوره صفویه(907 تا 1135 هجری قمری) متداول شد. از آن زمان تا اواسط قرن سیزدهم هجری قمری که جایگزین تقویم جلالی شد، بیشتر در امور دولتی و شرح وقایع تاریخی، در کنار تقویم های هجری قمری، جلالی و غیره استفاده می شد. در سال 1329 هجری قمری( مطابق 1289 هحری خورشیدی برجی) ، تقویم شمسی برجی به جای این تقویم رایج شد. سرانجام در سال 1304هجری شمسی که تقویم هجری شمسی به عنوان تقویم رسمی پذیرفته شد، به طور صریح استفاه از سالهای دوره 12 ساله حیوانی منسوخ شد. با وجود این، هنوز هم در بعضی از انواع تقویم های ایرانی، از نام سال هجری شمسی در دوره 12 ساله حیوانی استفاده می شود که از این پس در مقاله حاضر، به اختصار" نام سال هجری شمسی" نامیده می شود.

جدول تعیین نام سال هجری شمسی

این جدول توسط نگارنده مقاله حاضر طرح شده است و سه قسمت دارد. قسمت های فوقانی، راست و میانی، به ترتیب دو رقم سمت چپ، دو رقم سمت راست و نام سال هجری شمسی را مشخص می کنند. با استفاده از این جدول می توان نام سال، 2100 سال هجری شمسی(0-2099 ) را تعیین نمود. برای آشنایی با روش استفاده این جدول به ذکر مثال زیر می پرد ازیم.

مثال – نام سال 1370 هجری شمسی را تعیین می کنیم.
از قسمت های فوقانی و راست جدول به ترتیب اعداد 13 و 70 را مشخص می کنیم. از خانه های مربوط به اعداد یاد شده ، دو خط به ترتیب یکی به سمت پایین و دیگری به سمت چپ در نظر می گیریم. در قسمت میانی جدول، در خانه مربوط به تلاقی این دو خط، کلمه " گوسفند" نوشته شده است . بنابراین، نام سال 1370 هجری شمسی " گوسفند" است.

Building Services Handbook, Sixth Edition: Incorporating Current Building & Construction Regulations

تعداد صفحات : 720 | انگلیسی | 2011| 5 مگابایت | پی دی اف

10m Beam Centrifuge

The CUED 10m beam centrifuge is the main focus of centrifuge based geotechnical modelling at Cambridge. This machine has a 150g-tonne capacity, achieving a maximum centrifugal acceleration of approx. 130g at 4.125m radius. The beam centrifuge was built in the early 1970s to designs by Philip Turner. Further details on the design and construction of this centrifuge can be found in the article on Centrifuges in Soil Mechanics by Schofield and Turner. The large capacity of this centrifuge together with it's physical size give great scope for the building of novel experimental packages. Electrical and Hydraulic slip-rings are available for the passing of water, compressed air and power to packages, enabling complex actuators to be constructed and used. A great deal of experience has been accumulated over the past 40 years, enabling actuators for such diverse situations as creating earthquake loading and climatic fluctuations to be created. Large numbers of experiments have been carried out on the beam centrifuge over the last 40 years. At present, major projects include PhD projects on Earthquakes, Monopile foundations, Piling, Tunnelling and Retaining walls

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