The ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research. Referred to during development as the ZX81 Colour and ZX82, it was launched as the ZX Spectrum by Sinclair to highlight the machine's colour display, compared with the black and white of its predecessor, the ZX81; the Spectrum was released as eight different models, ranging from the entry level with 16 KB RAM released in 1982 to the ZX Spectrum +3 with 128 KB RAM and built in floppy disk drive in 1987. The Spectrum was among the first mainstream-audience home computers in the UK, similar in significance to the Commodore 64 in the US; the introduction of the ZX Spectrum led to a boom in companies producing software and hardware for the machine, the effects of which are still seen. Some credit it as the machine. Licensing deals and clones followed, earned Clive Sinclair a knighthood for "services to British industry"; the Commodore 64, Dragon 32, Oric-1, Oric Atmos, BBC Micro and the Amstrad CPC range were rivals to the Spectrum in the UK market during the early 1980s.
While the machine was discontinued in 1992, new software titles continue to be released – over 40 so far in 2018. The Spectrum is based on a Zilog Z80 A CPU running at 3.5 MHz. The original model has 16 KB of ROM and either 16 KB or 48 KB of RAM. Hardware design was by Richard Altwasser of Sinclair Research, the outward appearance was designed by Sinclair's industrial designer Rick Dickinson. Video output is through an RF modulator and was designed for use with contemporary television sets, for a simple colour graphic display. Text can be displayed using 32 columns × 24 rows of characters from the ZX Spectrum character set or from a set provided within an application, from a palette of 15 shades: seven colours at two levels of brightness each, plus black; the image resolution is 256×192 with the same colour limitations. To conserve memory, colour is stored separate from the pixel bitmap in a low resolution, 32×24 grid overlay, corresponding to the character cells. In practice, this means that all pixels of an 8x8 character block share one foreground colour and one background colour.
Altwasser received a patent for this design. An "attribute" consists of a foreground and a background colour, a brightness level and a flashing "flag" which, when set, causes the two colours to swap at regular intervals; this scheme leads to what was dubbed colour clash or attribute clash, where a desired colour of a specific pixel could not be selected. This became a distinctive feature of the Spectrum, meaning programs games, had to be designed around this limitation. Other machines available around the same time, for example the Amstrad CPC or the Commodore 64, did not suffer from this limitation; the Commodore 64 used colour attributes in a similar way, but a special multicolour mode, hardware sprites and hardware scrolling were used to avoid attribute clash. Sound output is through a beeper on the machine itself, capable of producing one channel with 10 octaves. Software was available that could play two channel sound; the machine includes an expansion bus edge connector and 3.5 mm audio in/out ports for the connection of a cassette recorder for loading and saving programs and data.
The "ear" port has a higher output than the "mic" and is recommended for headphones, with "mic" for attaching to other audio devices as line in. It was manufactured in Scotland, in the now closed Timex factory; the machine's Sinclair BASIC interpreter is stored in ROM and was written by Steve Vickers on contract from Nine Tiles Ltd. The Spectrum's chiclet keyboard is marked with BASIC keywords. For example, pressing "G" when in programming mode would insert the BASIC command GO TO; the BASIC interpreter was developed from that used on the ZX81 and a ZX81 BASIC program can be typed into a Spectrum unmodified, but Spectrum BASIC included many extra features making it easier to use. The ZX Spectrum character set was expanded from that of the ZX81, which did not feature lower-case letters. Spectrum BASIC included extra keywords for the more advanced display and sound, supported multi-statement lines; the cassette interface was much more advanced and loading around five times faster than the ZX81, unlike the ZX81, the Spectrum could maintain the TV display during tape storage and retrieval operations.
As well as being able to save programs, the Spectrum could save the contents of arrays, the contents of the screen memory, the contents of any defined range of memory addresses. Rick Dickinson came up with a number of designs for the "ZX82" project before the final ZX Spectrum design. A number of the keyboard legends changed during the design phase including ARC becoming CIRCLE, FORE becoming INK and BACK becoming PAPER; the Spectrum reused a number of design elements of the ZX81: The ROM code for things such as floating point calculations and expression parsing were similar. The simple keyboard decoding and cassette interfaces were nearly identical; the central ULA integrated circuit was somewhat similar although it implemented the major enhancement over the ZX81: A hardware based television raster generator that indirectly gave the new machine four times as much processing power as the ZX81 due to the Z80 now being released from this video generation task. A bug in the ULA as designed
Network analyzer (electrical)
A network analyzer is an instrument that measures the network parameters of electrical networks. Today, network analyzers measure s–parameters because reflection and transmission of electrical networks are easy to measure at high frequencies, but there are other network parameter sets such as y-parameters, z-parameters, h-parameters. Network analyzers are used to characterize two-port networks such as amplifiers and filters, but they can be used on networks with an arbitrary number of ports. Network analyzers are used at high frequencies. Special types of network analyzers can cover lower frequency ranges down to 1 Hz; these network analyzers can be used for example for the stability analysis of open loops or for the measurement of audio and ultrasonic components. The two basic types of network analyzers are scalar network analyzer —measures amplitude properties only vector network analyzer —measures both amplitude and phase propertiesA VNA is a form of RF network analyzer used for RF design applications.
A VNA may be called a gain-phase meter or an automatic network analyzer. An SNA is functionally identical to a spectrum analyzer in combination with a tracking generator; as of 2007, VNAs are the most common type of network analyzers, so references to an unqualified "network analyzer" most mean a VNA. Three prominent VNA manufacturers are Keysight and Rohde & Schwarz. Another category of network analyzer is the microwave transition analyzer or large signal network analyzer, which measure both amplitude and phase of the fundamental and harmonics; the MTA was commercialized before the LSNA, but was lacking some of the user-friendly calibration features now available with the LSNA. The basic architecture of a network analyzer involves a signal generator, a test set, one or more receivers and display. In some setups, these units are distinct instruments. Most VNAs have two test ports, permitting measurement of four S-parameters, but instruments with more than two ports are available commercially; the network analyzer needs a test signal, a signal generator or signal source will provide one.
Older network analyzers did not have their own signal generator, but had the ability to control a stand-alone signal generator using, for example, a GPIB connection. Nearly all modern network analyzers have a built-in signal generator. High-performance network analyzers have two built-in sources. Two built-in sources are useful for applications such as mixer test, where one source provides the RF signal, another the LO, or amplifier intermodulation testing, where two tones are required for the test; the test set takes the signal generator output and routes it to the device under test, it routes the signal to be measured to the receivers. It splits off a reference channel for the incident wave. In a SNA, the reference channel may go to a diode detector whose output is sent to the signal generator's automatic level control; the result is better control of better measurement accuracy. In a VNA, the reference channel goes to the receivers. Directional couplers or two resistor power dividers are used for signal separation.
Some microwave test sets include the front end mixers for the receivers. The receivers make the measurements. A network analyzer will have one or more receivers connected to its test ports; the reference test port is labeled R, the primary test ports are A, B, C.... Some analyzers will dedicate a separate receiver to each test port, but others share one or two receivers among the ports; the R receiver may be less sensitive than the receivers used on the test ports. For the SNA, the receiver only measures the magnitude of the signal. A receiver can be a detector diode; the simplest SNA will have a single test port, but more accurate measurements are made when a reference port is used. The reference port will compensate for amplitude variations in the test signal at the measurement plane, it is possible to share a single detector and use it for both the reference port and the test port by making two measurement passes. For the VNA, the receiver measures the phase of the signal, it needs a reference channel to determine the phase, so a VNA needs at least two receivers.
The usual method down converts the reference and test channels to make the measurements at a lower frequency. The phase may be measured with a quadrature detector. A VNA requires at least two receivers, but some will have three or four receivers to permit simultaneous measurement of different parameters. There are some VNA architectures that infer magnitude from just power measurements. With the processed RF signal available from the receiver / detector section it is necessary to display the signal in a format that can be interpreted. With the levels of processing that are available today, some sophisticated solutions are available in RF network analyzers. Here the reflection and transmission data is formatted to enable the information to be interpreted as as possible. Most RF network analyzers incorporate features including linear and logarithmic sweeps and log formats, polar plots, Smith charts, etc. Trace markers, limit lines and pass / fail criteria may be added in many instances. A VNA is a test system that enables the RF performance of radio frequency and microwave devices to be ch
Lectins are carbohydrate-binding proteins, macromolecules that are specific for sugar moieties of other molecules. They are known as phytohemagglutinins. Lectins perform recognition on the cellular and molecular level and play numerous roles in biological recognition phenomena involving cells and proteins. Lectins mediate attachment and binding of bacteria and viruses to their intended targets. Lectins are found in many foods; some foods such as beans and grains need to be fermented to reduce lectin content. Some lectins are beneficial, such as CLEC11A which promotes bone growth, while others may be powerful toxins such as ricin. Lectins may be disabled by specific mono- and oligosaccharides, which bind to ingested lectins from grains, nightshade plants and dairy; the selectivity of lectins means that they are useful for analyzing blood type, they are used in some genetically engineered crops to transfer traits, such as resistance to pests and resistance to herbicides. W. C. Boyd introduced term'lectin' in 1954 from Latin word'choose'.
Lectins occur ubiquitously in nature. They may bind to a soluble carbohydrate or to a carbohydrate moiety, a part of a glycoprotein or glycolipid, they agglutinate certain animal cells and/or precipitate glycoconjugates. Most lectins do not possess enzymatic activity. Lectins have the following functions in animals: The regulation of cell adhesion; the regulation of glycoprotein synthesis. The regulation of blood protein levels; the binding of soluble extracellular and intercellular glycoproteins. As a receptor on the surface of mammalian liver cells for the recognition of galactose residues, which results in removal of certain glycoproteins from the circulatory system; as a receptor that recognizes hydrolytic enzymes containing mannose-6-phosphate, targets these proteins for delivery to the lysosomes. I-cell disease is one type of defect in this particular system. Lectins are known to play important roles in the innate immune system. Lectins such as the MBL, the mannose-binding lectin, help mediate the first-line defense against invading microorganisms.
Other immune lectins play a role in self-nonself discrimination and they modulate inflammatory and autoreactive processes. Intelectins bind microbial may function in the innate immune system as well. Lectins may be involved in pattern recognition and pathogen elimination in the innate immunity of vertebrates including fishes; the function of lectins in plants is still uncertain. Once thought to be necessary for rhizobia binding, this proposed function was ruled out through lectin-knockout transgene studies; the large concentration of lectins in plant seeds decreases with growth, suggests a role in plant germination and in the seed's survival itself. The binding of glycoproteins on the surface of parasitic cells is believed to be a function. Several plant lectins have been found to recognize non-carbohydrate ligands that are hydrophobic in nature, including adenine, auxins and indole acetic acid, as well as water-soluble porphyrins, it has been suggested that these interactions may be physiologically relevant, since some of these molecules function as phytohormones.
It is hypothesized that some hepatitis C viral glycoproteins attach to C-type lectins on the host cell surface to initiate infection. To avoid clearance from the body by the innate immune system, pathogens express surface lectins known as adhesins and hemagglutinins that bind to tissue-specific glycans on host cell-surface glycoproteins and glycolipids. Purified lectins are important in a clinical setting; some of the glycolipids and glycoproteins on an individual's red blood cells can be identified by lectins. A lectin from Dolichos biflorus is used to identify cells. A lectin from Ulex europaeus is used to identify the H blood group antigen. A lectin from Vicia graminea is used to identify the N blood group antigen. A lectin from Iberis amara is used to identify the M blood group antigen. A lectin from coconut milk is used to identify Theros antigen. A lectin from Carex is used to identify R antigen. In neuroscience, the anterograde labeling method is used to trace the path of efferent axons with PHA-L, a lectin from the kidney bean.
A lectin from bananas inhibits HIV-1 in vitro. Achylectins, isolated from Tachypleus tridentatus, show specific agglutinating activity against human A-type erythrocytes. Anti-B agglutinins such as anti-BCJ and anti-BLD separated from Charybdis japonica and Lymantria dispar are of value both in routine blood grouping and research. Lectins from legume plants, such as PHA or concanavalin A, have been used as model systems to understand the molecular basis of how proteins recognize carbohydrates, because they are easy to obtain and have a wide variety of sugar specificities; the many crystal structures of legume lectins have led to a detailed insight of the atomic interactions between carbohydrates and proteins. Concanavalin A and other commercially available lectins have been used in affinity chromatography for purifying glycoproteins. In general, proteins may be characterized with respect to glycoforms and carbohydrate structure by means of affinity chromatography, affinity electrophoresis, affinity immunoelectrophoreis with lectins as well as in microarrays, as in evanescent-field fluorescence-assisted lectin microarray.
One example of the powerful biological at
Spherical nucleic acid
Spherical nucleic acids – defined as structures that are an arrangement of densely packed oriented nucleic acids in a spherical geometry – were first introduced in 1996 by the Mirkin group at Northwestern University. The arrangement and orientation of one-dimensional linear nucleic acids within this three-dimensional framework results in new chemical and physical properties in the use of nucleic acids for intracellular gene regulation, molecular diagnostics, materials synthesis applications; the first SNA consisted of 3’ alkanethiol-terminated, single-stranded oligonucleotides covalently attached to the surface of spherical gold nanoparticles. A dense nucleic acid loading was achieved through a series of salt additions, in which positively charged counterions were used to reduce electrostatic repulsion between adjacent negatively charged DNA strands and thereby enable more efficient DNA packing onto the nanoparticle surface. One- and two-dimensional forms of nucleic acids are important biological machinery for the storage and transmission of genetic information.
Underlying this utility are the bioprogrammable interactions between complementary nucleotide bases. Scientists and engineers have been synthesizing and, in certain cases, mass-producing such structures for decades in an effort to understand and exploit this elegant recognition motif; the recognition abilities of nucleic acids are enhanced when arranged in a spherical geometry, which allows for polyvalent interactions. This polyvalency, along with the high density and degree of orientation described above, helps to explain why a three-dimensional nucleic acid structure composed of linear, one-dimensional nucleic acids exhibits different properties than its lower-dimensional constituents. Two decades of research on SNAs have revealed that they combine properties from the inorganic core and the nucleic acid shell; the inorganic nanoparticle core serves two purposes: 1) it imparts upon the conjugate novel physical and chemical properties, 2) it acts as a scaffold for the assembly and orientation of nucleic acids.
The nucleic acid shell gives the conjugate chemical and biological recognition abilities that offer greater binding strengths and higher duplex stabilities compared to the same sequence of linear DNA, cooperative melting behavior with DNA strands of a complementary sequence, enhanced cellular uptake without the use of transfection agents. Recent studies have shown that one can crosslink the DNA strands at their base, subsequently dissolve the inorganic core with KCN or I2 to create a coreless form of SNA, which exhibits many of the properties of the original DNA-nanoparticle conjugate. Due to their structure and function, SNAs occupy a materials space distinct from "DNA nanotechnology and origami." With DNA origami, such structures are synthesized via DNA hybridization events. In contrast, the SNA structure can be synthesized independent of nucleic acid sequence and hybridization, instead relying upon chemical bond formation between nanoparticles and nucleic acid adsorbates. Furthermore, DNA origami uses DNA hybridization interactions to realize a final structure, whereas SNAs and other forms of three-dimensional nucleic acids utilize the nanoparticle core to arrange the linear nucleic acid components into functional forms.
Indeed, it is the particle core that dictates the shape of the SNA, to date, single-stranded and double-stranded versions of these materials have been created that consist of DNA, LNA, RNA. SNAs should not be confused with their monovalent analogues – individual particles coupled to a single DNA strand; such single strand-nanoparticle conjugate structures have led to interesting advances in their own right, but do not exhibit the unique properties of SNAs. SNAs have been proposed as nanotherapeutics. Despite their high negative charge, these nanostructures are taken up by cells, without the need for positively charged polymeric co-carriers, are effective as gene regulation agents in both siRNA and antisense gene regulation pathways; the proposed mechanism is that, unlike their linear counterparts, SNAs have the ability to complex scavenger proteins and thereby facilitate endocytosis. Investigation of the mechanism for SNA uptake revealed that enzymatic degradation is reduced as compared to a linear oligonucleotide.
These materials have been suggested for a wide variety of therapeutic treatments which are developed by the company Exicure. The first clinical trial, in collaboration with Purdue Pharma, focused on SNA AST-005 for chronic plaque psoriasis, it showed no toxicity but no significant efficacy and Purdue Pharma has notified Exicure it has declined to exercise its option to develop AST-005 at this time. SNAs packed gold nanoparticles are able to deliver small interfering RNA to treat glioblastoma multiforme in a proof-of-concept study using mouse model, reported by the research team led by Mirkin; the iRNA targets silences the oncogene. The gold nanoparticles injected intravenously cross the blood-brain barrier and find their target in the brain. In the animal model, the treatment caused a 20% increase in survival rate and 3 to 4 fold reduction in tumor size. Mirkin indicated that this novel therapeutic approach establishes a platform for treating a wide range of diseases; the Mirkin group has proposed spherical nucleic acids as novel labels
The Social-National Assembly of Ukraine was an assemblage of the ultra-nationalist and neo-Nazi radical organizations and groups founded in 2008 that share the social-national ideology and agree upon building a social-national state in Ukraine. It is located on the far right of the Ukrainian politics and built around the "Patriot of Ukraine". In late November 2013 both the S. N. A. and the "Patriot of Ukraine" entered in an association with several other Ukrainian far-right groups which led to the formation of the Right Sector. The S. N. A. is reported to be close to Svoboda, Yuriy Zbitnyev, the leader of the nationalist political party "Nova Syla". The S. N. A.'s activities are Kiev-based. The S. N. A. was founded in 2008 and maintained relations with the wider social-nationalist movement in Ukraine. In the late 2000s, Ukrainian president Victor Yushchenko and the Our Ukraine bloc bolstered the S. N. A. and other far-right groups by supporting an explicitly nationalist view of Ukrainian history. Following the 2009 death of Maksym Chaika, an S.
N. A member, killed in a fight with antifascists in Odessa, Yushchenko supported the far-right interpretation of Chaika's death, describing him and others as heroes and victims driven to violence for a just cause. In 2010, the Ukrainian Helsinki Human Rights Union reported on attacks by the S. N. A and "Patriot of Ukraine" against Vietnamese and other foreign market stalls in Vasylkiv. Most attacks were carried out by youth and targeted Vietnamese and Gypsies. According to the S. N. A website, they replaced them with Ukrainians; the S. N. A states; that year, Ukrainian authorities shut down an S. N. A music festival near Kiev that promoted neo-Nazism and chauvinism among Ukrainian youth; the music glorified Nazi aesthetics and the harassment of minorities. In August 2011, the Netherlands Institute of Human Rights warned about the growth of extremist organizations including the S. N. A and "Patriot of Ukraine", noting repeated attacks against visible minorities; the institute noted the government's inability or unwillingness to deal with extreme-right movements in Ukraine.
In August 2011 Ukrainian police announced that they thwarted a bomb attack planned for the commemoration of Ukrainian Independence. The "Patriot of Ukraine", a part of the S. N. A, declared that some of their members had been detained by police but maintained no connection with any terrorist plan. Spokespersons for the S. N. A and "Patriot of Ukraine" insisted that criminal action against them was a pretext for SBU repression against their organizations. In 2013, the S. N. A, "Patriot of Ukraine" and Autonomous Resistance all increased in popularity, contributing to the growth of Svoboda as well; the Social National Assembly helped to create an umbrella radical organization - the Right Sector. Other radical anti-semitic groups operating in Ukraine including the "White Hammer" and "C14", a neo-Nazi wing of Svoboda, joined it. During the 2014 Ukrainian revolution, the militants from the S. N. A and the "Patriot of Ukraine" were on the front lines of the street riots in Kiev. According to Igor Krivoruchko, the leader of the Kiev's S.
N. A. Branch, its members started clashes with the police near the Presidential Administration Building and initiated the Hrushevskoho Street riots, they seized and burned on 18 February 2014 the central office of the ruling party - the Party of Regions - in Kiev. A bystander, 57-year-old IT engineer who tried to stop the attackers from entering the server room, was beaten to death. Oleh Odnoroshenko, the S. N. A and "Patriot of Ukraine" ideologue and one of the "Right Sector" leaders, stated in February 2014 that the "Right Sector" would be hesitant to enter into the government following the departure of Viktor Yanukovych. Odnoroshenko thought that the politicians would try to use the Right Sector credibility and popularity while pursuing their own agendas. At the end of April 2014, S. N. A members marched with burning torches to the Independence Square and came into conflict with the Self-defense of the Maidan units. During the fight, the S. N. A. and Self-defense of the Maidan activists used rubber bullet guns and tear gas, ambulances arrived to treat wounded.
Oleh Odnoroshenko volunteered to the press that the S. N. A members organized the attack on the Russian embassy in Kiev on 14 June 2014. In March 2014 the Social-National Assembly created Azov Battalion. In April, members were wounded in combat against separatists in eastern Ukraine. During the first week of May, Kiev began delivering weapons. On 6 May, the Azov Battalion captured; the next day the S. N. A. announced that it was interrogating the captive, Radical Party leader Oleh Lyashko posted photographs of him naked and bound. Lyashko confirmed that Azov had captured some other separatist leaders. On 13 June, the Azov Battalion stormed separatists' barricades in Mariupol and seized control of the city center after a six-hour battle; the group has been assigned to prevent arms smuggling. According to the founder of the organization, Biletsky states that Social-Nationalism is based on three pillars: Racism and Great Power; the ideology stands in a strong opposition to any form of democracy. Under Socialism in Social Nationalist ideology means third position in economics, authoritative power, fair distribution among national producers.
According to Biletsky, the main distinction between Nazism and Social Nationalism is the fact that Nazism is more socialist, while Social Nationalism is more national
United States Naval Aviator
A Naval Aviator is a commissioned officer or warrant officer qualified as a pilot in the United States Navy, United States Marine Corps or United States Coast Guard. In the U. S. Navy, most Naval Aviators are unrestricted line officers, eligible for command at sea. A small number of URL officers trained as Naval Aviators and Naval Flight Officers who hold technical degrees at the undergraduate and/or postgraduate level may opt to laterally transfer to the restricted line as Aerospace Engineering Duty Officers. AEDOs are test pilot school graduates and retain their flying status, with most of their billets being in the Naval Air Systems Command. An smaller number of Naval Aviators are in the U. S. Navy Medical Corps as Naval Flight Surgeons; these are either former URL officers designated as Naval Aviators who attend medical school and transfer to the Medical Corps, or an smaller percentage of "dual designator" Naval Flight Surgeons who are selected to be Student Naval Aviators and undergo pilot training as Medical Corps officers.
The vast majority of Naval Flight Surgeons, although they are on flight status, are not dual designated and are not Naval Aviators. All U. S. Marine Corps officers are line officers, either unrestricted line, limited duty, or warrant officer, eligible to command MAGTF units commensurate with their grade and occupational specialty. S. Marine Corps does not have restricted line officers or staff corps officers, as does the U. S. Navy. All current USMC naval aviators and naval flight officers are unrestricted line officers, analogous to the Navy's URL officers; the U. S. Coast Guard categorizes all of its officers with its naval aviators being considered "operational" officers in the same manner as its cutterman officers in the Coast Guard's surface cutter fleet; until 1981, the U. S. Navy and U. S. Marine Corps had a small number of senior enlisted personnel trained as pilots; such individuals were referred to as naval aviation pilots, colloquially "NAPs" or "APs." The since retired NAPs continue to have a professional organization known as the Silver Eagles, which remains informally aligned with other naval aviation professional organizations such as the Association of Naval Aviation, the Tailhook Association, the Maritime Patrol Association, the Naval Helicopter Association, among others.
The naval aviation pilot wings worn by NAPs were identical in design to the naval aviator insignia worn by commissioned officers. The Silver Eagle title was a reflection; the U. S. Navy still has an unknown number of senior officers on active duty in the Regular Navy or serving in the Navy Reserve who were accessed as NAVCADs; these individuals entered service via the NAVCAD program during the mid/late 1980s and early 1990s when the program was reinstated following a hiatus of over twenty years. NAVCADs were non-commissioned cadets who were required to have a minimum of 60 college credit hours to enter flight training and were accessed only through the now defunct Aviation Officer Candidate School program. Upon completion of AOCS, NAVCADS would enter into flight training and upon successful completion of training and designation as a naval aviator would be commissioned as officers with a reserve commission in an active duty status. After completion of their initial operational flying tour, they would receive an assignment to complete their bachelor's degree.
NAVCADs who failed to complete flight training were contractually obligated to enter fleet service as undesignated enlisted personnel. The last civilian applicants were accepted into the NAVCAD program in 1992 and the program was canceled on October 1, 1993. Except for an small number of enlisted personnel selected to attend flight school subsequent to completing the STA-21, OCS, USMMA, USNA or USCGA programs, all other student naval aviators must first obtain an officer commission. To become a naval aviator, non-prior service personnel must be between the ages of 19 and 27 when entering flight training. Adjustments can be made up to 24 months for those with prior service, up to 48 months for those in the military at the time of application or for Marine Corps platoon leader's course applicants with prior enlisted service. Navy and Marine Corps officers are commissioned through five sources: the United States Naval Academy at Annapolis, Maryland. A smaller number were commissioned via the Navy's limited duty officer or chief warrant officer programs, but this track has since been discontinued.
Coast Guard Officers receive their commissions either from the United States Coast Guard Academy or Coast Guard Officer Candidate School, both located in New London, Connecticut. Graduates of these programs are commissioned as Navy ensigns in the U. S. Navy or U. S. Coast Guard, or as second lieutenants in the Marine Corps. All individuals must p
Social network analysis
Social network analysis is the process of investigating social structures through the use of networks and graph theory. It characterizes networked structures in terms of nodes and the ties, edges, or links that connect them. Examples of social structures visualized through social network analysis include social media networks, memes spread, information circulation and acquaintance networks, business networks, social networks, collaboration graphs, disease transmission, sexual relationships; these networks are visualized through sociograms in which nodes are represented as points and ties are represented as lines. These visualizations provide a means of qualitatively assessing networks by varying the visual representation of their nodes and edges to reflect attributes of interest. Social network analysis has emerged as a key technique in modern sociology, it has gained a significant following in anthropology, demography, communication studies, geography, information science, organizational studies, political science, social psychology, development studies and computer science and is now available as a consumer tool.
Social network analysis has its theoretical roots in the work of early sociologists such as Georg Simmel and Émile Durkheim, who wrote about the importance of studying patterns of relationships that connect social actors. Social scientists have used the concept of "social networks" since early in the 20th century to connote complex sets of relationships between members of social systems at all scales, from interpersonal to international. In the 1930s Jacob Moreno and Helen Jennings introduced basic analytical methods. In 1954, John Arundel Barnes started using the term systematically to denote patterns of ties, encompassing concepts traditionally used by the public and those used by social scientists: bounded groups and social categories. Scholars such as Ronald Burt, Kathleen Carley, Mark Granovetter, David Krackhardt, Edward Laumann, Anatol Rapoport, Barry Wellman, Douglas R. White, Harrison White expanded the use of systematic social network analysis. In the study of literature, network analysis has been applied by Anheier and Romo, Wouter De Nooy, Burgert Senekal.
Indeed, social network analysis has found applications in various academic disciplines, as well as practical applications such as countering money laundering and terrorism. Homophily: The extent to which actors form ties with similar versus dissimilar others. Similarity can be defined by gender, age, educational achievement, values or any other salient characteristic. Homophily is referred to as assortativity. Multiplexity: The number of content-forms contained in a tie. For example, two people who are friends and work together would have a multiplexity of 2. Multiplexity has been associated with relationship strength. Mutuality/Reciprocity: The extent to which two actors reciprocate each other's friendship or other interaction. Network Closure: A measure of the completeness of relational triads. An individual's assumption of network closure is called transitivity. Transitivity is an outcome of the situational trait of Need for Cognitive Closure. Propinquity: The tendency for actors to have more ties with geographically close others.
Bridge: An individual whose weak ties fill a structural hole, providing the only link between two individuals or clusters. It includes the shortest route when a longer one is unfeasible due to a high risk of message distortion or delivery failure. Centrality: Centrality refers to a group of metrics that aim to quantify the "importance" or "influence" of a particular node within a network. Examples of common methods of measuring "centrality" include betweenness centrality, closeness centrality, eigenvector centrality, alpha centrality, degree centrality. Density: The proportion of direct ties in a network relative to the total number possible. Distance: The minimum number of ties required to connect two particular actors, as popularized by Stanley Milgram's small world experiment and the idea of'six degrees of separation'. Structural holes: The absence of ties between two parts of a network. Finding and exploiting a structural hole can give an entrepreneur a competitive advantage; this concept was developed by sociologist Ronald Burt, is sometimes referred to as an alternate conception of social capital.
Tie Strength: Defined by the linear combination of time, emotional intensity and reciprocity. Strong ties are associated with homophily and transitivity, while weak ties are associated with bridges. Groups are identified as'cliques' if every individual is directly tied to every other individual,'social circles' if there is less stringency of direct contact, imprecise, or as structurally cohesive blocks if precision is wanted. Clustering coefficient: A measure of the likelihood that two associates of a node are associates. A higher clustering coefficient indicates a greater'cliquishness'. Cohesion: The degree to which actors are connected directly to each other by cohesive bonds. Structural cohesion refers to the minimum number of members who, if removed from a group, would disconnect the group. Visual representation of social networks is important to understand the network data and convey the result of the analysis. Numerous methods of visualization for data produced by social network analysis have been presented.
Many of the analytic software have modules for network visualization. Exploration of