All the observed semileptonic interactions are well described in the lowest order by the interaction Hamiltonian, which relates the lepton currents to the weak hadronic current containing the vector and axial parts:

where We note that they enter the lepton current on an equal footing, which corresponds to the -universality hypothesis. In what follows, the symbol I will be used to denote or and the symbol for the corresponding neutrino or

Let us consider semileptonic processes of the type where are hadron systems. In the lowest order, the transition amplitude is

where the states are determined only by strong interactions. This expression is similar to formula (2.5), which describes the process The matrix element of the lepton weak current is again singled out as a simple and well-known factor, and all the complexity of strong interactions lies in the matrix element from the hadronic current. Semileptonic reactions "probe" hadronic states with the help of a current operator. For decay processes, the structure is the same as described above, except for the obvious replacement of the neutrino spinor with an antineutrino spinor. Note that, according to the agreement we have adopted, the current increases electric charge hadrons per unit: In processes where the charge of hadrons decreases by one, the matrix element from the conjugate operator contributes, the lepton current, of course, must also undergo corresponding changes.

As in the case of the electromagnetic current, at the present time it is not possible to specify a method for constructing weak currents from fundamental hadronic fields. Let us try to describe the properties of currents in the most general view, so that the consequences do not depend on the details of the construction. Of course, it is possible that special models can lead to a good idea. In fact, this is exactly what happened with the ideas of the algebra of currents. As already mentioned, it is known that with respect to Lorentz transformations it behaves like a sum

vector and axial: In some processes, for example, only the vector part contributes; in others, for example, only and for the rest, for example, both parts. Currents conserve baryon charge. As for strangeness, and contain parts that preserve strangeness and change it by one, are correlated: It is possible that there are other currents, say with or but since there are no experimental confirmations for them, we will not consider these possibilities. In relation to the isospin, it is considered that currents with are transformed as a charge-increasing component of the isovector, and currents with as a charge-increasing component of the iso-doublet. Apparently, terms with other properties with respect to the isotopic spin are not required. Therefore, for all well-established currents, we can write:

The properties of the currents with respect to the change in the third isospin component can be omitted, since they follow from the relation recorded, no, and that all new factors can be included in the currents. Later, we will discuss some ideas that will allow us to more accurately define the concept of scale and give the angle an objective meaning. Now we note that the angle is called the Cabibbo angle.

For currents without a change in strangeness (vector and axial), we introduce one more attribute by which they can be classified. This is parity, which is characterized by an isotopic rotation around the second axis by an angle that changes the sign and the charge conjugation operation, which also changes the sign. Generally speaking, it is not necessary that and and also belong to the same multiplet. But if, nevertheless, the currents and their conjugate currents enter the same multiplet, then they can be assigned a certain -parity: or It is known that the vector current c is even with respect to the -transformation, and the axial current is odd. There is currently no room for alternative possibilities. Recall that the isovector part of the electromagnetic current has and the isoscalar part

The isovector part of the electromagnetic current is thus the neutral component of the isotopic triplet with

Whereas the charge-increasing and charge-reducing terms, generally speaking, are of another isotopic triplet. It can be assumed that in fact it is one and the same triplet. This is the famous CVC conjecture of Gerstein-Zeldovich, Feynman and Gell-Man. It has received some experimental confirmation and leads (if it is really correct) to significant simplifications. It is known that electromagnetic currents, isoscalar and isovector, are stored separately. The CVC hypothesis is so named because it requires the conservation of the vector current without changing the strangeness: Now, with the help of isotopic symmetry, one can relate the corresponding matrix elements for For example, for -mesons at rest. content.

The properties of weak and electromagnetic currents with respect to isotopic transformations and hypercharge are now fully defined. But one more symmetry of strong interactions remains, namely, It is not a strict symmetry. But assuming that it is not violated very much, the question arises as to how the various currents are transformed under the action of For all the currents that we have already discussed, the simplest possibility, consistent with isotopy and hypercharge, is that they are transformed as members of the -octet. However, Cabibbo suggested something stronger, namely that all vector currents (weak and electromagnetic) are included in one common octet. Then the isoscalar electromagnetic current is a triplet of electromagnetic and weak strangeness-preserving currents, as well as weak currents with a change in strangeness, are transformed under the action in the same way as Cabibbo also assumed that all axial weak currents belong to one octet of axial operators. These hypotheses, if correct, lead to enormous simplifications, since only two independent objects remain to be studied: the vector and axial octets. In each of them, various members are connected to each other. This means, in particular, that the relative scale per octet is fixed. Moreover, the absolute scale is also fixed in the vector octet, since this octet contains the charge and hypercharge operators. Now, it seems, it only remains to fix the scale of the axial octet with respect to the vector octet, which, however, is difficult to do for objects that have different transformation properties with respect to the Lorentz transformation. Nevertheless, ambiguity remains - after all, there is not quite a strict symmetry of strong interactions. Is it possible to give -properties such a meaning that will be preserved even if violated found a solution to both problems. This will be discussed below.

The very weak current /c f is not taken into account in this figure. When approaching f / c 0, when / ce becomes much larger than all the other components, the resulting current increases rapidly.

The measurement of very low currents is technically difficult problem. Therefore, it is difficult to register individual particles with the help of an ionization chamber, and it is usually included in integrated systems intended for registering particle or γ-ray fluxes.

Continuous charging with very low currents is used not only to replenish the internal losses of the battery, but also to compensate for intermittent discharges of small magnitude.

They respond to very weak currents, sometimes only thousandths of an ampere, and are 10 to 20 times more sensitive than conventional electromagnetic devices.

Electrochemical detectors register a very weak current that occurs when chlorine interacts with an electrolyte. Colorimetric sensors use photocell signals that determine the color intensity of a reagent that changes color when interacting with chlorine.

A very weak current passing through this resistance, say, one microampere (10 - a), will create a voltage Ucl-JR on this resistance according to Ohm's law. In our example, this voltage is equal to one volt. But with such a change in the grid voltage, the anode current changes by 2–3 mA. Therefore, a change in current through the grid resistance by 1 μA causes a change in the anode current several thousand times greater. We thus amplify the initial very weak current by several thousand times, delivering the necessary energy through the operation of the anode battery.

These electrometer tubes allow very low currents of the order of a few microamperes, a slope of the order of several microamperes per volt, and a gain of the order of unity.

In this case, they work with very weak currents of 0 1 ca, which makes this method suitable for all common solvents, with the exception of hydrocarbons.

At the same time, they work with very low currents of about 0-1 mA, which makes it possible to use this method for the distillation of all common solvents with the exception of hydrocarbons.

In this case, they work with very weak currents of 0 1 (ha), which makes this method suitable for all common solvents, with the exception of hydrocarbons.

A sensitive galvanometer is needed to measure the very low current flowing in the chamber. This method, however, requires additional time for processing photographic materials, and at present, some models of polarographs use galvanometers paired with a recording device.

Along with electricity and light, low currents and low-current wiring provide comfort and convenience in our home. The voltage in low-current systems is 12-24 V, while the current strength is measured in milliamps. Today, not a single house or room can be imagined without low-voltage networks. Since these wires with low voltage provide us with telephone, Internet, television, uninterrupted operation of computers. In other words, low-voltage systems are systems for receiving terrestrial and satellite television, a telephone network and the Internet, video surveillance systems, fire alarms, intercoms, local networks and a distribution cable network, as well as wire broadcasting systems (radio).

It should be said that installation of low-voltage networks must be carried out in parallel with other internal engineering systems. At the same time, it is necessary to pay attention to some nuances that are important in the quality and uninterrupted provision of communication, Internet, television, video surveillance and security services. For example, low-current cables are required to be run at least 0.5 m from power cables to prevent electromagnetic interference and the negative effects of unbalanced currents. The intersection of low-current cables with power cables should be at an angle of 900. Low-current cables laid outside the premises and buildings must be protected from mechanical damage with metal overlays. Distribution boxes on the wall must be located at least 300 mm from the ceiling. In addition, junction boxes should not be installed above windows, openings and doors.

In addition, a low-current wiring route, for example, from a junction box to a telephone must be straight and shortest. In addition, open wiring along the walls should be at a height of more than 50 mm from the ceiling and 25-30 mm from the floor. It should be said that open laying is carried out in cable channels and is usually not practiced in dwellings. Hidden wiring can be carried out through the channels of embedded devices of a convenient height. Hidden wiring is carried out in strobes along the walls, in PVC sleeves under the raised floor and in floor screed, behind false ceilings. In this case, low-current sockets are mounted on walls or in floor hatches.

Wiring to the end device must be done with a solid wire, without splicing. To exclude the impact of radio transmissions on telephone conversations, a certain distance must be maintained between the wires of the telephone network and wire broadcasting (radio) laid in a common box. For example, with a line length of 10 m, the distance should be at least 15 mm, 50 mm with a length of 70 m. In addition, low-current lines of television and video surveillance systems must be grounded to protect against atmospheric discharges and unbalanced mains currents.

After tracing a low-current system, you must perform covert work plan. On this plan, it is required to depict the entire route of the low-current system in the room, the location of all junction boxes and outlets. The presence of such a plan will greatly facilitate the implementation of subsequent repair and installation work in the room.

WEAK CURRENTS

small currents used in telegraph, telephone, signaling, and other similar installations (S. t. installations).

• - see Diadynamic ...

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"WEAK CURRENTS" in books

natural electric currents