Relational database

RC Circuits An RC circuit is a circuit with both a resistor (R) and a capacitor (C). RC circuits are freqent element in electronic devices. They also play an important role in the transmission of electrical signals in nerve cells. A capacitor can store energy and a resistor placed in series with it will control the rate at which it charges or discharges. We will confine our studies to the following circuit, in which the switch can be moved between positions a and b. Let us begin by reviewing some facts about capacitors: When a capacitor of capacitance C is in series with a battery of voltage Vb and a resistor of resistance R, the voltage drops must be: which is a statement that the voltage gained going across the battery must equal the voltage drop across the capacitor plus the voltage drop across the resistor. Discharging the capacitor: The capacitor initially is connected (switch in position a) for a long time, and is then disconnected by moving the switch to b at time t = 0.

ring of charge Electric Field on the Axis of a Ring of Charge [Note from ghw: This is a local copy of a portion of Stephen Kevan's lecture on Electric Fields and Charge Distribution of April 8, 1996.] We determine the field at point P on the axis of the ring. It should be apparent from symmetry that the field is along the axis. The field dE due to a charge element dq is shown, and the total field is just the superposition of all such fields due to all charge elements around the ring. The perpendicular fields sum to zero, while the differential x-component of the field is We now integrate, noting that r and x are constant for all points on the ring: This gives the predicted result. Electric Field on the Axis of a Uniformly Charged Disk Using the above result, we can easily derive the electric field on the axis of a uniformly charged disk, simply by invoking superposition and summing up contributions of a continuous distribution of rings, as shown in the following figure from Tipler:

List of relational database management systems From Wikipedia, the free encyclopedia This is a list of relational database management systems. List of Software[edit] Historical[edit] Relational by the Date-Darwen-Pascal Model[edit] Current[edit] Obsolete[edit] See also[edit] Physics For Idiots - Electromagnetism Charge comes in 2 types, positive and negative and is measured in Coulombs (C). If you have a charge on its own it emits a field in all directions. The field from a charge is represented by E as in E lectricity. If you put another charge in the field it experiences a force. The q's are the two charges and r2 is the distance between them squared. Stuff Moving As soon as a charge starts to move it produces another field. Which is known as the Lorentz force. But we can already describe one of these bits, qE is just Coulombs Law so only half the work left to do. This is where its gets a little harder. Also, at A-level or below the situation will probably be simplified so you only have to consider the E and B fields separately. Obviously F is the force and q is charge, E and B are the two fields previously described and v is the velocity of the moving charge. Circuits A circuits is basically just a series of moving charges with the occasional object or device in the way that affects the flow.

Physicist proposes method to teleport energy (PhysOrg.com) -- Using the same quantum principles that enable the teleportation of information, a new proposal shows how it may be possible to teleport energy. By exploiting the quantum energy fluctuations in entangled particles, physicists may be able to inject energy in one particle, and extract it in another particle located light-years away. The proposal could lead to new developments in energy distribution, as well as a better understanding of the relationship between quantum information and quantum energy. Japanese physicist Masahiro Hotta of Tohoku University has explained the energy teleportation scheme in a recent study posted at arxiv.org, called “Energy-Entanglement Relation for Quantum Energy Teleportation.” Previously, physicists have demonstrated how to teleport the quantum states of several different entities, including photons, atoms, and ions. In quantum energy teleportation, a physicist first makes a measurement on each of two entangled particles.

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Study: China’s ‘Great Firewall’ may not actually isolate Internet users The researchers' visualization of "culturally defined markets" -- the interconnected, language- and geography-based groups into which Internet users naturally separate. The clearest markets in this diagram are English (white), Chinese (red), Japanese (green) and Russian (fuscia). (Northwestern University) Everyone from Hillary Clinton to Amnesty International has bashed China’s “Great Firewall” as an impediment to free speech and democracy. That’s what makes a new study out of Northwestern University both odd and intriguing: According to its authors, media researchers Harsh Taneja and Angela Xiao Wu, Chinese censorship actually has little impact on what people there read online, and Chinese Internet users aren’t particularly isolated, even vis-a-vis users in countries with unrestricted access. What’s more, they essentially argue, the Internet isn’t that grand, global community that connects and equalizes everyone.

Ten Common Database Design Mistakes No list of mistakes is ever going to be exhaustive. People (myself included) do a lot of really stupid things, at times, in the name of “getting it done.” This list simply reflects the database design mistakes that are currently on my mind, or in some cases, constantly on my mind. I have done this topic two times before. Before I start with the list, let me be honest for a minute. So, the list: Poor design/planning Ignoring normalization Poor naming standards Lack of documentation One table to hold all domain values Using identity/guid columns as your only key Not using SQL facilities to protect data integrity Not using stored procedures to access data Trying to build generic objects Lack of testing Poor design/planning “If you don’t know where you are going, any road will take you there” – George Harrison Prophetic words for all parts of life and a description of the type of issues that plague many projects these days. Ignoring Normalization Are there always 12 payments? Maintainability

PostgreSQL: The world's most advanced open source database The Workshops Of Everything TokyoBound Ito Seiyu (1882-1961) has been pushing the envelope of kinbaku and torture imagery long before the “Golden Age” of SM magazines, getting some of his better work censored and banned by the authorities, earning him the label of “pervert”. To help you better appreciate this series, first read the following notes on the kanji characters heading each picture and text: Wood (木, ki), Fire (火, hi), Earth (土, tsuchi), Metal (金, kin), and Water (水, mizu) are the “five elements” called Wu Xing (五行) in Chinese. The concepts of Wu Xing can be found anywhere from acupuncture to feng shui (geomancy) to martial arts, and even apply to tea ceremony. Sun (日, hi) and Moon (月, tsuki) plus the five Wu Xing elements also correspond to the days of the week. There goes hardly a description of beauty that doesn’t include the combination of the three kanji characters for Snow (雪, yuki), Moon (月, tsuki), and Flower (花, hana). Now, let’s cut to the chase and enjoy the first installment. Sun 日 (hi) Moon 月 (tsuki) Fire Water

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