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. 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: Such a surface charge density is conventionally given the symbol sigma. where Q is the total charge and R is the radius of the disk. and thus a charge given by The field produced by this ring of charge is along the x-axis and is given by the previous result: The total field is given by simply integrating over a from 0 to R
Relational database In the relational model, each table schema must identify a column or group of columns, called the primary key, to uniquely identify each row. A relationship can then be established between each row in the table and a row in another table by creating a foreign key, a column or group of columns in one table that points to the primary key of another table. The relational model offers various levels of refinement of table organization and reorganization called database normalization. (See Normalization below.) The database management system (DBMS) of a relational database is called an RDBMS, and is the software of a relational database. In relational databases, each data item has a row of attributes, so the database displays a fundamentally tabular organization. Relational databases are both created and queried by DataBase Management Systems (DBMSs). Terminology[edit] Relational database terminology. Relations or Tables[edit] Tuples by definition are unique. Base and derived relations[edit]
Découverte d’un texte proto-massorétique (500 AD) | Didier Fontaine C’est une découverte historique. Un témoin du texte biblique, vieux de 1500 ans, vient d’être mis au jour. D’après l’Autorité des Antiquités Israéliennes (IAA) : this is the most ancient scroll from the five books of the Hebrew Bible to be found since the Dead Sea scrolls, most of which are ascribed to the end of the Second Temple period (first century BCE-first century CE) A vrai dire la découverte a été faite il y a une quarantaine d’années dans une arche sainte de la synagogue d’Ein Gedi, mais comme le rouleau en question est entièrement carbonisé, son déchiffrement n’a pu intervenir que récemment, grâce à de nouvelles techniques informatiques permettant de réaliser une copie numérique 3D haute résolution du rouleau, puis… le dérouler virtuellement (source). Wow ! Or les premiers mots déchiffrés révèlent les huit premiers versets du premier chapitre du Lévitique. Le problème avec les manuscrits de la mer Morte, c’est qu’ils sont de nature différente.
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. What’s more, they essentially argue, the Internet isn’t that grand, global community that connects and equalizes everyone. Claims that firewalls like China’s isolate users, they write, “are based on an assumption that Internet users would use all websites if given access. But let’s step back for a moment and consider the methodology behind these surprising findings. Those overlaps gradually surfaced a number of interconnected clusters, each corresponding to a corner of the Internet most popular among a certain group.
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. This produces a characteristic time dependence that turns out to be exponential. 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. Decide what the charge across the capacitor was just before the switch was thrown.
Jupiter et les Astrologues – One360.eu Lorsqu’il s’identifie à Jupiter, Emmanuel Macron a sans doute en tête la mythologie antique gréco-babylonienne, pour qui Jupiter est le roi des dieux. Nous savons qu’une partie de l’élite illuminée utilise l’astrologie et la mythologie pour coder des évènements, des manifestations sportives, etc.. Bien que les croyances associées à l’astrologie restent populaires, la découverte de nouvelles planètes au 18ème siècle change la donne et a amené certains astrologues à redistribuer les maîtrises planétaires, l’astrologie s’est aussi adaptée aux nouvelles limites entre les constellations de 1922 et à la précession des équinoxes avec l’astrologie sidérale, notamment en Asie. Il faut comprendre que certains évènements n’arrivent pas à cause de l’alignement des planètes et des signes, ils sont programmés à l’avance. Les étoiles et les constellations expliquent nos civilisations. Les Centaures représentent la civilisation, bien qu’ils se battent parfois entre eux.
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. If you’re interested in hearing the podcast version, visit Greg Low’s super-excellent SQL Down Under. 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 Ignoring Normalization Are there always 12 payments? Poor naming standards Security
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. Like charges repel and unlike charges attract. 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 Which is Which? If you set up all your component in a closed loop like so
The Workshops Of Everything