29 Eylül 2011 Perşembe

Demon Core

The Demon core was the nickname given to a 6.2-kilogram (14 lb) subcritical mass of plutonium that accidentally went briefly critical in two separate accidents at the Los Alamos laboratory in 1945 and 1946. Both incidents resulted in the acute radiation poisoning and the subsequent death of a scientist. After these incidents, the sphere of plutonium was referred to as the Demon Core.

The core was used in an atomic bomb test in 1946, five weeks after the second fatal accident, and proved in practice to have a slightly increased yield over similar cores which had not been subjected to criticality excursions.

First incident

On August 21, 1945, the plutonium core produced a burst of neutron radiation that caught Harry Daghlian in its path. Daghlian was a physicist who made a mistake while working alone performing neutron reflection experiments on the core. The core was placed within a stack of neutron-reflective tungsten carbide bricks, and the addition of each brick moved the assembly closer to criticality. While attempting to stack another brick around the assembly Daghlian accidentally dropped it onto the core and thereby caused the core to go critical. Despite quick action in moving the brick off the assembly, Daghlian received a fatal dose of radiation. He died 25 days later from acute radiation poisoning.

Another person who was in the lab at the time of the accident—Private Robert J. Hemmerly, a Special Engineer Detachment (SED) guard—received an exposure of approximately 31 roentgens of soft X-rays (80 kV equivalent) and less than 1 roentgen of gamma rays. Hemmerly died in 1978 (33 years after the accident) from acute myelogenous leukemia at the age of 62.

Second Incident

On May 21, 1946, physicist Louis Slotin and seven other scientists were in a Los Alamos laboratory conducting an experiment to verify the exact point at which a subcritical mass (core) of fissile material could be made critical by the positioning of neutron reflectors. The test was known as "tickling the dragon's tail" for its extreme risk. It required the operator to place two half-spheres of beryllium (a neutron reflector) around the core to be tested and manually lower the top reflector over the core via a thumb hole on the top. As the reflectors were manually moved closer and farther away from each other, scintillation counters measured the relative activity from the core. Allowing them to close completely would result in the instantaneous formation of a critical mass and a lethal power excursion. Under Slotin's unapproved protocol, the only thing preventing this was the blade of a standard flathead screwdriver, manipulated by the scientist's other hand. Slotin, who was given to bravado, became the local expert, performing the test almost a dozen separate times, often in his trademark bluejeans and cowboy boots, in front of a roomful of observers. Enrico Fermi reportedly told Slotin and others they would be "dead within a year" if they continued performing it.

While lowering the top reflector, Slotin's screwdriver slipped a fraction of an inch, allowing the top reflector to fall into place around the core. Instantly there was a flash of blue light and a wave of heat across Slotin's skin; the core had become supercritical, releasing a massive burst of neutron radiation. He quickly knocked the two halves apart, stopping the chain reaction and likely saving the lives of the other men in the laboratory. Slotin's body positioning over the apparatus also shielded the others from much of the neutron radiation. He received a massively lethal dose in under a second and died nine days later from acute radiation poisoning. The nearest physicist to Slotin, Alvin C. Graves, was watching over Slotin's shoulder and was thus partially shielded by him, receiving a high but non-lethal radiation dose. Graves was hospitalized for several weeks with severe radiation poisoning, developed chronic neurological and vision problems as a result of the exposure, suffered a significant shortening of his lifespan and died of a radiation-induced heart attack 20 years later. The other six people in the room were far enough away from the assembly to avoid fatal injury, but they all suffered other complications as a result of the accident. Two people suffered severe shortening of their lives and died years later from radiation induced complications: leukemia (at age 42, 18 years after the accident) and clinical aplastic anemia.

Demon Core In Use

The Demon core was put to use for the Able detonation test of the Crossroads series on July 1, 1946, demonstrating that the criticality experiments of Daghlian and Slotin increased the efficiency of the weapon.

1 Temmuz 2011 Cuma

Dark Flow

Dark flow is an astrophysical term describing a peculiar velocity of galaxy clusters. The actual measured velocity is the sum of the velocity predicted by Hubble's Law plus a small and unexplained (or dark) velocity flowing in a common direction.

According to standard cosmological models, the motion of galaxy clusters with respect to the cosmic microwave background should be randomly distributed in all directions. However, analyzing the three-year WMAP data using the kinematic Sunyaev-Zel'dovich effect, the authors of the study found evidence of a "surprisingly coherent" 600–1000 km/s flow of clusters toward a 20-degree patch of sky between the constellations of Centaurus and Vela.

The authors (Alexander Kashlinsky, F. Atrio-Barandela, D. Kocevski, and H. Ebeling) suggest that the motion may be a remnant of the influence of no-longer-visible regions of the universe prior to inflation. Telescopes cannot see events earlier than about 380,000 years after the big bang, when the universe became transparent (the Cosmic Microwave Background); this corresponds to the particle horizon at a distance of about 46 billion (4.6×10^10) light years. Since the matter causing the net motion in this proposal is outside this range, it would in a certain sense be outside our visible universe; however, it would still be in our past light cone.

The results appeared in the October 20, 2008, issue of Astrophysical Journal Letters. Since then, the authors have extended their analysis to additional clusters and the recently released WMAP five-year data.


The dark flow was determined to be flowing in the direction of the Centaurus and Hydra constellations. This corresponds with the direction of the Great Attractor, which was a previous gravitational mystery originally discovered in 1973. However, the source of the Great Attractor's attraction was thought to originate from a massive cluster of galaxies called the Norma cluster, situated merely between 150-250 million light-years away. This may reveal that the source of that attraction might lie even further away, and which the Great Attractor itself is heading towards.

In a study from March 2010, Kashlinsky extended his work from 2008, by using the 5-year WMAP results rather than the 3-year results, and doubling the number of galaxy clusters observed from 700. The team also sorted the cluster catalog into four "slices" representing different distance ranges. They then examined the preferred flow direction for the clusters within each slice. While the size and exact position of this direction display some variation, the overall trends among the slices exhibit remarkable agreement. "We detect motion along this axis, but right now our data cannot state as strongly as we'd like whether the clusters are coming or going," Kashlinsky said.

The team has so far catalogued the effect as far out as 2.5 billion light-years, and hope to expand their catalog out further still to twice the current distance.

Panoramic view of galaxies beyond Milky Way, with Norma cluster & Great Attractor shown by a long blue arrow at the bottom-right in image near the disk of the Milky Way.

NASA's Goddard Space Center confirmed this could be the effects of a sibling universe or a region of space-time fundamentally different from the observable universe. Data on more than 1,000 galaxy clusters have been measured, including some as distant as 3 billion light-years. Alexander Kashlinsky claims these measurements show the universe's steady flow is clearly not a statistical fluke. Said Kashlinsky: "At this point we don't have enough information to see what it is, or to constrain it. We can only say with certainty that somewhere very far away the world is very different than what we see locally. Whether it's 'another universe' or a different fabric of space-time we don't know."

Sloan Great Wall

The Sloan Great Wall is a giant wall of galaxies (a galactic filament) and to the present day is the largest known structure in the universe. Its discovery was announced on October 20, 2003 by J. Richard Gott III of Princeton University and Mario Jurić and their colleagues, based on data from the Sloan Digital Sky Survey.

The wall measures 1.37 billion light years (1.30×1025 m) in length, which is approximately 1/60 of the diameter of the observable universe, and is located approximately one billion light-years from Earth.

The Sloan Great Wall, classified as the supercluster SCl 126 in SIMBAD, is nearly three times longer than the CfA2 Great Wall of galaxies, the previous record-holder, which was discovered by Margaret Geller and John Huchra of Harvard in 1989.

23 Mayıs 2011 Pazartesi

Flexible organic light-emitting diode (FOLED)

A flexible organic light emitting diode (FOLED) is a type of organic light-emitting diode (OLED) incorporating a flexible plastic substrate on which the electroluminescent organic semiconductor is deposited. This enables the device to be bent or rolled while still operating. Currently the focus of research in industrial and academic groups, flexible OLEDs form one method of fabricating a rollable display.

An OLED emits light due to the electroluminescence of thin films of organic semiconductors approximately 100 nm thick. Regular OLEDs are usually fabricated on a glass substrate, but by replacing glass with a flexible plastic such as polyethylene terephthalate (PET) among others, OLEDs can be made both bendable and lightweight.

Such materials may not be suitable for comparable devices based on inorganic semiconductors due to the need for lattice matching and the high temperature fabrication procedure involved.

In contrast, flexible OLED devices can be fabricated by deposition of the organic layer onto the substrate using a method derived from inkjet printing, allowing the inexpensive and roll-to-roll fabrication of printed electronics.

Flexible OLEDs may be used in the production of rollable displays, electronic paper, or bendable displays which can be integrated into clothing, wallpaper or other curved surfaces. Prototype displays have been exhibited by companies such as Sony, which are capable of being rolled around the width of a pencil.

6 Mart 2011 Pazar

Chengdu J-20

The Chengdu J-20 (simplified Chinese: 歼二十; traditional Chinese: 殲二十; pinyin: Jiān èr shí; literally "Annihilator Twenty") is a fifth generation stealth, twin-engine fighter aircraft prototype developed by Chengdu Aircraft Industry Group for the Chinese People's Liberation Army Air Force. In late 2010, the J-20 underwent high speed taxiing tests. The J-20 made its first flight on 11 January 2011. General He Weirong, Deputy Commander of the People's Liberation Army Air Force said in November 2009 that he expected the J-20 to be operational in 2017–2019.

The J-20 was one of the stealth fighter programs under the codename J-XX that was launched in the late 1990s. It has been also designated “Project 718”. Two prototypes (#2001-01 & #2001–02) have been built as of the end of 2010.

On 22 December 2010, the J-20 was under-going high speed taxiing tests outside the Chengdu Aircraft Design Institute with no confirmed flight tests. The J-20 made its first flight, which lasted about 20 minutes, on 11 January 2011.

Sukhoi PAK FA

The Sukhoi PAK FA (Russian: Перспективный авиационный комплекс фронтовой авиации, Perspektivny aviatsionny kompleks frontovoy aviatsii, literally "Prospective Airborne Complex - Frontline Aviation") is a fifth-generation jet fighter being developed by Sukhoi OKB for the Russian Air Force.

The current prototype is Sukhoi's T-50. The PAK FA, when fully developed, is intended to be the successor to the MiG-29 and Su-27 in the Russian inventory and serve as the basis of the Sukhoi/HAL FGFA project being developed with India. A fifth generation jet fighter, the T-50 performed its first flight 29 January 2010. Its second flight was on 6 February and its third on 12 February 2010. As of 31 August 2010, it had made 17 flights and by mid-November, 40 in total. The second prototype was to start its flight test by the end of 2010, but this was delayed until March 2011.


Although most of information about the PAK FA is classified, it is believed from interviews with people in the Russian Air Force and Defense Ministry that it will be stealthy, have the ability to supercruise, be outfitted with the next generation of air-to-air, air-to-surface, and air-to-ship missiles, incorporate a fix-mounted AESA radar with a 1,500-element array and have an "artificial intellect".

According to Sukhoi, the new radar will reduce pilot load and the aircraft will have a new data link to share information between aircraft.

Composites are used extensively on the T-50 and comprise 25% of its weight and almost 70% of the outer surface.It is estimated that titanium alloy content of the fuselage is 75%. Sukhoi's concern for minimizing radar cross-section (RCS) and drag is also shown by the provision of two tandem main weapons bays in the centre fuselage, between the engine nacelles. Each is estimated to be between 4.9-5.1 m long. The main bays are augmented by bulged, triangular-section bays at the wing root.

The Moskovsky Komsomolets reported that the T-50 has been designed to be more maneuverable than the F-22 Raptor at the cost of making it less stealthy than the F-22. One of the design elements that have such an effect is the Leading Edge Vortex Controller (LEVCON).


The PAK-FA SH121 radar complex includes three X-Band AESA radars located on the front and sides of the aircraft. These will be accompanied by L-Band radars on the wing leading edges. Band radars are proven to have increased effectiveness against very low observable (VLO) targets which are optimized only against X-Band frequencies, but their longer wavelengths reduce their resolution.

The PAK-FA will feature an IRST optical/IR search and tracking system, based on the OLS-35M which is currently in service with the Su-35S.

Hindustan Aeronautics Limited will reportedly provide the navigation system and the mission computer.


The PAK FA was expected to use a pair of Saturn 117S engines on its first flights. The 117S (AL-41F1A) is a major upgrade of the AL-31F based on the AL-41F intended to power the Su-35BM, producing 142 kN (32,000 lb) of thrust in afterburner and 86.3 kN (19,400 lb) dry. In fact, PAK FA already used a completely new engine in its first flight, as stated by NPO Saturn. The engine is not based on the Saturn 117S and is rumoured to be called "127 engine". The engine generates a larger thrust and has a complex automation system, to facilitate flight modes such as maneuverability. Exact specifications of the new engine are still secret. It is expected that each engine will be able to independently vector its thrust upwards, downward or side to side. Vectoring one engine up with the other one down can produce a twisting force. Therefore the PAK FA would be the first fifth generation fighter with full 3-D thrust vectoring along all three aircraft axes: pitch, yaw and roll. These engines will incorporate infrared and RCS reduction measures.

17 Ocak 2011 Pazartesi

Axial Precession

In astronomy, axial precession is a gravity-induced, slow and continuous change in the orientation of an astronomical body's rotational axis. In particular, it refers to the gradual shift in the orientation of Earth's axis of rotation, which, like a wobbling top, traces out a cone in a cycle of approximately 26,000 years (called a Great or Platonic Year in astrology). The term "precession" typically refers only to this largest secular motion; other changes in the alignment of Earth's axis — nutation and polar motion — are much smaller in magnitude.

Earth's precession was historically called precession of the equinoxes because the equinoxes moved westward along the ecliptic relative to the fixed stars, opposite to the motion of the Sun along the ecliptic. This term is still used in non-technical discussions, that is, when detailed mathematics are absent. Historically, Hipparchus is credited with discovering precession of the equinoxes. The exact dates of his life are not known, but astronomical observations attributed to him by Ptolemy date from 147 BC to 127 BC.

With improvements in the ability to calculate the gravitational force between planets during the first half of the 19th century, it was recognized that the ecliptic itself moved slightly, which was named planetary precession as early as 1863, while the dominant component was named lunisolar precession. Their combination was named general precession instead of precession of the equinoxes. Lunisolar precession is caused by the gravitational forces of the Moon and Sun on Earth's equatorial bulge, causing Earth's axis to move with respect to inertial space. Planetary precession (actually an advance) is due to the small angle between the gravitational force of the other planets on Earth and its orbital plane (the ecliptic), causing the plane of the ecliptic to shift slightly relative to inertial space. Lunisolar precession is about 500 times larger than planetary precession. In addition to the Moon and Sun, the other planets also cause a small movement of Earth's axis in inertial space, making the contrast in the terms lunisolar versus planetary misleading, so in 2006 the International Astronomical Union recommended that the dominant component be renamed the precession of the equator and the minor component be renamed precession of the ecliptic, but their combination is still named general precession.


The precession of the Earth's axis has a number of observable effects. First, the positions of the south and north celestial poles appear to move in circles against the space-fixed backdrop of stars, completing one circuit in 25,771.5 years (2000 rate). Thus, while today the star Polaris lies approximately at the north celestial pole, this will change over time, and other stars will become the "north star". As the celestial poles shift, there is a corresponding gradual shift in the apparent orientation of the whole star field, as viewed from a particular position on Earth.

Secondly, the position of the Earth in its orbit around the Sun at the solstices, equinoxes, or other time defined relative to the seasons, slowly changes. For example, suppose that the Earth's orbital position is marked at the summer solstice, when the Earth's axial tilt is pointing directly towards the Sun. One full orbit later, when the Sun has returned to the same apparent position relative to the background stars, the Earth's axial tilt is not now directly towards the Sun: because of the effects of precession, it is a little way "beyond" this. In other words, the solstice occurred a little earlier in the orbit. Thus, the tropical year, measuring the cycle of seasons (for example, the time from solstice to solstice, or equinox to equinox), is about 20 minutes shorter than the sidereal year, which is measured by the Sun's apparent position relative to the stars. Note that 20 minutes per year is approximately equivalent to one year per 25,771.5 years, so after one full cycle of 25,771.5 years the positions of the seasons relative to the orbit are "back where they started". (In actuality, other effects also slowly change the shape and orientation of the Earth's orbit, and these, in combination with precession, create various cycles of differing periods; see also Milankovitch cycles. The magnitude of the Earth's tilt, as opposed to merely its orientation, also changes slowly over time, but this effect is not attributed directly to precession.)

For identical reasons, the apparent position of the Sun relative to the backdrop of the stars at some seasonally fixed time, say the vernal equinox, slowly regresses a full 360° through all twelve traditional constellations of the zodiac, at the rate of about 50.3 seconds of arc per year (approximately 360 degrees divided by 25,771.5), or 1 degree every 71.6 years.

13 Ocak 2011 Perşembe


Android is a mobile operating system initially developed by Android Inc. Android was bought by Google in 2005. Android is based upon a modified version of the Linux kernel. Google and other members of the Open Handset Alliance collaborated on Android's development and release. The Android Open Source Project (AOSP) is tasked with the maintenance and further development of Android. Unit sales for Android OS smartphones ranked first among all smartphone OS handsets sold in the U.S. in the second and third quarters of 2010, with a third quarter market share of 43.6%.

Android has a large community of developers writing application programs ("apps") that extend the functionality of the devices. There are currently over 200,000 apps available for Android. Android Market is the online app store run by Google, though apps can be downloaded from third party sites (AT&T only permits third party apps on their Aria phone). Developers write primarily in the Java language, controlling the device via Google-developed Java libraries.] Python, Ruby and other languages are also available for Android development via the Android Scripting Environment.

The unveiling of the Android distribution on 5 November 2007 was announced with the founding of the Open Handset Alliance, a consortium of 79 hardware, software, and telecom companies devoted to advancing open standards for mobile devices. Google released most of the Android code under the Apache License, a free software and open source license.

The Android operating system software stack consists of Java applications running on a Java based object oriented application framework on top of Java core libraries running on a Dalvik virtual machine featuring JIT compilation. Libraries written in C include the surface manager, OpenCore media framework, SQLite relational database management system, OpenGL ES 2.0 3D graphics API, WebKit layout engine, SGL graphics engine, SSL, and Bionic libc. The Android operating system consists of 12 million lines of code including 3 million lines of XML, 2.8 million lines of C, 2.1 million lines of Java, and 1.75 million lines of C++.

2.3 (Gingerbread) Based on Linux Kernel

Updated user interface design
Support for extra-large screen sizes and resolutions (WXGA and higher)
Native support for SIP VoIP telephony
Support for WebM/VP8 video playback, and AAC audio encoding
New audio effects such as reverb, equalization, headphone virtualization, and bass boost
Support for Near Field Communication
System-wide copy–paste functionalities
Redesigned multi-touch software keyboard
Enhanced support for native code development
Audio, graphical, and input enhancements for game developers
Concurrent garbage collection for increased performance
Native support for more sensors (such as gyroscopes and barometers)
A download manager for long running downloads
Improved power management and application control
Native support for multiple cameras
Switched from YAFFS to the ext4 filesystem

Community-based firmware

There is a community of open-source enthusiasts that build and share Android-based firmware with a number of customizations and additional features, such as FLAC lossless audio support and the ability to store downloaded applications on the microSD card. This usually involves rooting the device. Rooting allows users root access to the operating system, giving more control over their environment variables. In order to use custom firmwares the devices bootloader must be unlocked. Rooting alone does not allow the flashing of custom firmware. Modified firmwares allow users of older phones to use applications available only on newer releases.

Those firmware packages are updated frequently, incorporate elements of Android functionality that haven't yet been officially released within a carrier-sanctioned firmware, and tend to have fewer limitations. CyanogenMod and VillainROM are two examples of such firmware.

On 24 September 2009, Google issued a cease and desist letter to the modder Cyanogen, citing issues with the re-distribution of Google's closed-source applications within the custom firmware. Even though most of Android OS is open source, phones come packaged with closed-source Google applications for functionality such as the application store and GPS navigation. Google has asserted that these applications can only be provided through approved distribution channels by licensed distributors. Cyanogen has complied with Google's wishes and is continuing to distribute this mod without the proprietary software. He has provided a method to back up licensed Google applications during the mod's install process and restore them when it is complete.

1 Ocak 2011 Cumartesi


Plex (also known as "Plexapp" or "Plex Media Center") is a partially open-source freeware media player for Intel-based Apple Macintosh computers. It has a 10-foot user interface design for the living-room TV. Its source code was initially forked from XBMC Media Center on May 21, 2008 which Plex today uses as an application framework platform for its GUI (Graphical User Interface) and media player part of their software. Similar to XBMC and Boxee, it is an alternative to Apple's Front Row for Mac, with skinnable and user-configurable interface.

Plex integrates content from iTunes and iPhoto (from the iLife software suite) as well as allows the user to manage all video, photos, music, and podcasts from a computer, optical disk, local network, and the Internet using an Apple or Harmony remote control. In 2009 the developers added their own 'app store' digital distribution platform called "Plex Online" with a growing list of community driven plugins for online content like Hulu, Netflix, and CNN video that are being distributed via "Plex Media Server" application which runs as a standa-alone software and media management interface.

Plex began as a free software hobby project but since 2010 has evolved into a (freeware) project that is owned and developed by a single for-profit startup company, (Plex, Inc.). It is a high tech company based in the United States that is responsible for the development of the Plex front-ends and back-end, its client–server model, and all accompanying software under the "Plex" trademark, as well as the exclusive copyright of the closed source software/code parts for both commercial and non-commercial use.

Plex supports a wide range of multimedia formats and includes features such as playlists, audio visualizations, slideshows, weather forecasts reporting, and an expanding array of third-party plugins. As a media center, Plex can play most audio and video file formats, as well as display images from many sources, including CD/DVD-ROM drive, USB flash drives, the Internet, and local area network shares. DVD playback is not yet fully integrated and requires the use of helper applications like Apple's DVD Player.

Through the processing power of modern Mac computer hardware, Plex is able to decode high-definition video up to 1080p. For older Macintosh computers, the software does not however support any hardware accelerated video decoding which means that users require a 2 GHz Intel Core 2 processor to decode the majority of 1080p videos encoded with the H.264 codec. Newer Apple models using Nvidia 9400M/GT320M/GT330M chipsets and Snow Leopard OS 10.6.3 or later does however benefit from H.264 hardware accelerated video decoding meaning that most of the decoding process is offloaded to the GPU.

Through its plugin system, Plex includes features such as YouTube and Apple movie trailer support, SHOUTcast, and more. Most plugin content (such as the Hulu and Netflix) is provided via a separate helper program called Plex Media Server, while some use an integrated Python runtime engine and plugin framework.

Plex Media Server is from closed source (contains proprietary code), however the other parts of Plex media center software are open-sourced and distributed under the GNU General Public License. Plex's open source code is hosted on GitHub. Plex media center and media player source code was initially based upon XBMC Media Center, which it uses as its application framework. The founder of Plex, Elan Feingold, was actually part of the official XBMC development team for a short while, but tension over the rest of XBMC's developers' strict adherence to the GPL and their open-source software mindset was one of the factors that led Elan (Plex founder) to leave the XBMC project and create the Plex fork.