V-type systems

Zhu and Scully [32] have shown that quantum interference in a V-type system, driven by a laser held from an auxiliary level, can lead to the elimination of the spectral line at the driving laser frequency. 

Figure 3. Three-level V-type system driven from an auxiliary level.

We have shown in Section V.A.2 that a laser field can drive the V-type system into the antisymmetric (trapping) state through the coherent interaction between the symmetric and antisymmetric states. Akram et al. [24] have shown that in the A system there are no trapping states to which the population can be transferred by the laser field. This can be illustrated by calculating the transition dipole moments between the dressed states of the driven A system. The procedure of calculating the dressed states of the A system is the same as for the V system. The only difference is that now the eigenstates of the unperturbed Hamiltonian Ho are 3, N - 1), 1,N), 2,N), and the dressed states are given by... 

An alternative method in which one could create a V-type system with parallel or antiparallel dipole moments is to apply a strong laser field to one of the two transitions in a A-type atom. The scheme is shown in Fig. 18. When the dipole moments of the 11) —> 3) and 2) —> 3) transitions are perpendicular, the laser exclusively couples to the 2) —> 3) transition and produces dressed states... 

Figure 18. Laser induced V-type system with nondegenerate transitions. A laser field applied to the 12) —> 3) transition of a A system creates nondegenerate dressed states separated by fl = a+ A[. The subsystem with the upper dressed atates a), b) and the ground state 1) behaviors as a V-type system with parallel dipole moments.

Two-photon processes can also be modified using CC. It is possible to selectively inhibit or enhance two-photon absorption by phase modulation [166-168] and other interference techniques [169, 170]. It is also possible to use CC to induce population trapping and gain in V-type systems [171,172]. Furthermore, it has been realized that interference between one-photon and N-photon transitions results in FIT in atomic systems [173-175]. 

With decreasing My B ratio, two or three B zigzag chains are connected at bonding distances, thus forming double or triple chains (Fig. 1). This tendency toward two-dimensional boron net formation (i.e., AlBj type) is recognized from the structural series within the V-B system VnB +, = (n - 1) VB -I- VBj (n = 1,2,3,5 not known for n = 4). ... 

Phase transitions are not restricted to P — V — T systems and may occur in other types of system. Well-known transitions occur in magnetic systems,... 

The results previously shown for sucrose emphasize that selectivity of thionocarbamate formation is dependent on the configuration and structure of the sugar. Thus the /ra .v-decalin-type system is easily formed on the glucopyran form, whereas the isothiocyanate linked to the fructofuran moiety remains inactive even if the presence of triethylamine in DMF at 80 °C (Scheme 8).37... 

As a final example, we may mention the NaCl-type phases formed in the V-0 systems. The V01 x phase is homogeneous in the composition range 42-57 at.% O. Lattice parameter determination in combination with density measurements evidenced that, in the structure, vacancies occur in both V and O sublattices through the entire range of composition. At the stoichiometric composition VO there are = 15% of sites vacant in each sublattice. 

Cooperative enzyme systems in which the presence of an allosteric effector results in an alteration of the ymax value of the system (as opposed to changes in the value(s) K systems). See Vmax-Type (or, V-Type) Allosteric System Allosterism... 

Velocity-modulated allosteric regulation, V, ,-TYPE ALLOSTERIC SYSTEM VENOM EXONUCLEASE Venom phosphodiesterase, PHOSPHODIESTERASES VESICLE TRANSPORT IN CELLS Vibrational bond stretching mode,... 

SRECIFICITY CONSTANT V -TYPE (or, V-TYPE) ALLOSTERIC SYSTEM... 

Vmax-TYPE (or V-Type Allosteric System) ALLOSTERISM... 

Accordingly over all the composition range from MX to MX2, either the NiAs- or Cdl2-type structure is stable at higher temperatures. A number of papers have been published on 3d-transition metal chalcogenides from the viewpoint of order-disorder of metal vacancies. A study of the V-S system from this point of view is described here. 

Figure 9.6 Areas of existence of different V species in a composition diagram for the Cr(Fe)/V/Sb/0 rutile-type system [46d].

Figure 1.106 Mixing length and mixing time for the V-type micro mixer with vertical interdigital arrangement for two gas systems (Ar-N2 and He-N2) to be mixed [Pfeifer et al., Chem. Ing. Tech. 76, 5 (2004) 607],...

The abundance of cyclic tetrapyrroles in the bacterial reaction center naturally suggests the preparation of triads bearing two porphyrin moieties. A number of such systems have been described. Building upon their earlier work with D-A type systems [19, 66], Sanders, Beddard and coworkers have reported triad 14, which consists of two doubly-linked porphyrins, one of which bears a pyromellitimide acceptor [66]. The pyromellitimide moiety is nearly as good an electron acceptor as benzoquinone (E0 = —0.55 V vs. —0.51 V for benzoquinone). Triad 14,... 

The V-type (or vacuolar-type) H+-ATPase was first found in fungal vacuoles and plant tonoplasts,13 l4) and is now known to be widely distributed in mammalian endomembrane systems.15) Like F-type ATPase, the subunit structure of the V-type ATPase is complicated. The membrane extrinsic sector is composed of 73 kDa, 58 kDa, 38 kDa, and 34 kDa subunits, while the membrane intrinsic sector is composed of 40 kDa 20 kDa and 16 kDa subunits. 

Towards the end of this section it may be worthwhile to point out some new reactions with high-valent metals and TBHP. The first is a pyridinium dichromate PDC-TBHP system. Nonsubstituted or alkyl-substituted conjugated dienes, such as 1,3-cyclooctadiene (87) and others (also linear dienes), yield keto allyl peroxides 88 (equation 18), whereas phenyl-substituted dienes such as 1,4-diphenylbutadiene (89) gave diketo compounds, 90 (equation 19). In further research into a GIF-type system with iron and TBHP, limonene gave a mixture of products with carvone as the major product. The mechanism is thought to proceed initially by formation of a Fe(V)-carbon... 

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