Nucleons are composed of up quarks and down quarks, and the weak force allows a quark to change its flavour by emission of a W boson leading to creation of an electron/antineutrino or positron/neutrino pair. For either electron or positron emission to be energetically possible, the energy release ( see below) or Q value must be positive.īeta decay is a consequence of the weak force, which is characterized by relatively lengthy decay times. The binding energies of all existing nuclides form what is called the nuclear band or valley of stability. The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy. By this process, unstable atoms obtain a more stable ratio of protons to neutrons. Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay, but are created in the decay process. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in so-called positron emission. Proton-antineutrino collision: p + ν̄ e → n + e +Įlectrons and protons are of course attracted by the electromagnetic interaction between them, but if they collide the weak interaction can make this interaction happen.In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. Neutron-neutrino collision: n + ν e → p + e – There’s a very low probability of a neutrino interacting with matter, but here’s what happens when they do: You get an antineutrino in β – decay and a neutrino in β + decay so that lepton number is conserved. RULES FOR DRAWING FEYNMAN DIAGRAMSġ) Incoming particles start at the bottom of the diagram and move upwards.Ģ) The Baryons stay on one side of the diagram, and the leptons stay on the other side.ģ) The W bosons carry charge from one side of the diagram to the other – make sure charges balance.Ĥ) A W – particle going to the left has the same effect as a W + particle going to the right. You can draw Feynman diagrams for loads of interactions but you only need to learn the ones in this post for your exam. He worked out a really neat way of solving problems by drawing pictures rather than doing calculations.ġ) Gauge bosons are represented by wiggly lines (technical term).Ģ) Other particles are represented by straight lines. Richard Feynman was a brilliant physicist who was famous for explaining complicated ideas in a fun way that actually made sense. Creating a virtual W particle uses so much energy that it can only exist for a very short time and it can’t travel far.Ģ) On the other hand, the photon has zero mass, which gives you a force with infinite range.įeynman Diagrams Show What’s Going In and What’s Coming Out The Larger the Mass of the Gauge Boson, the Shorter the Range of the Forceġ) The W bosons have a mass of about 100 times that of a proton, which gives the weak force a very short range. The graviton may exist but there’s no evidence for it. Gravity only really matters when you’ve got big masses like stars and planets. Particle physicists never bother about gravity because it’s so incredibly feeble compared to other types of interaction. Each one has its own gauge boson and you have to learn their names: Type of Interaction Gauge bosons are virtual particles – they only exist for a very short time.Īll forces in nature are caused by four fundamental forces. The repusion between two protons is caused by the exchange of virtual photons, which are the gauge bosons of the electromagnetic force. These exchange particles are called gauge bosons. Particle exchange also explains attraction, but you need a bit more imagination.Ģ) Attraction – Each time the boomerang is thrown or caught the people get pushed together. It happens because the ball carries momentum. That’s the idea behind exchange particles.ġ) Repulsion – Each time the ball is thrown or caught the people get pushed apart. So, when two particles interact, something must happen to let one particle know that the other one’s there. You can’t have instant action at a distance (according to Einstein, anyway). To the casual observer, this might not seem entirely fair. Having learnt about hadrons (baryons and mesons) and leptons, antiparticles and quarks, you now have the esteemed privilege of learning about yet another weirdy thing called the gauge boson.
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![]() It has a non‑blocking, event‑driven architecture that copes with huge amounts of requests without a noticeable increase in resource utilization. NGINX is designed to be a “shock absorber” for your site or application. Inherent Protection of the NGINX Event‑Driven Architecture These features address a DDoS attack both by regulating the incoming traffic and by controlling the traffic as it is proxied to backend servers. NGINX and NGINX Plus have a number of features that – in conjunction with the characteristics of a DDoS attack mentioned above – can make them a valuable part of a DDoS attack mitigation solution. Using NGINX and NGINX Plus to Fight DDoS Attacks ![]() The Referer header is sometimes set to a value you can associate with the attack.The User-Agent header is sometimes set to a non‑standard value.Because the traffic is generated by bots and is meant to overwhelm the server, the rate of traffic is much higher than a human user can generate. ![]() However, the number of connections and requests from a forward proxy is typically much lower than in a DDoS attack. The use of forward proxies can also create this pattern, because the forward proxy server’s IP address is used as the client address for requests from all the real clients it serves. Note: It’s important not to assume that this traffic pattern always represents a DDoS attack. As a result, each IP address is responsible for many more connections and requests than you would expect from a real user. The traffic normally originates from a fixed set of IP addresses, belonging to the machines used to carry out the attack. Because these attacks are carried out by bots rather than actual users, the attacker can easily open large numbers of connections and send large numbers of requests very rapidly.Ĭharacteristics of DDoS attacks that can be used to help mitigate against them include the following (this is not meant to be an exhaustive list): Other attacks can take the form of sending a large number of requests or very large requests. For example, for systems that don’t handle large numbers of concurrent connections well, merely opening a large number of connections and keeping them active by periodically sending a small amount of traffic can exhaust the system’s capacity for new connections. Application‑Layer DDoS Attack CharacteristicsĪpplication‑layer (Layer 7/HTTP) DDoS attacks are carried out by software programs ( bots) that can be tailored to best exploit the vulnerabilities of specific systems. Typically, the attacker tries to saturate a system with so many connections and requests that it is no longer able to accept new traffic, or becomes so slow that it is effectively unusable. Of course, in case you would be logging all resources of your site (images, css, js, etc), it would be really easy to get to those numbers as a normal user.A Distributed Denial‑of‑Service (DDoS) attack is an attempt to make a service, usually a website, unavailable by bombarding it with so much traffic from multiple machines that the server providing the service is no longer able to function correctly because of resource exhaustion. ![]() # 240 pages in 60 seconds, or 4p/s average, is suspicious) # Based on apache-badbots but a simple IP check (any IP requesting more than In our jail.local, we have (at the end of the file): If this regex matches, the line is ignored. # Notes.: Regexp to catch a generic call from an IP address. # Generated on Fri Jun 08 12:09: by BeezNest New filter in /etc/fail2ban/nf: # Fail2Ban configuration file |
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