Alternating Cycles

In XPS, chemical information is comparatively slowly acquired in a stepwise fashion along with the depth, with alternate cycles of sputtering and analysis. Examples of profiles through oxide films on pure iron and on Fe-12Cr-lMo alloy are shown in Fig. 2.9, in which the respective contributions from the metallic and oxide components of the iron and chromium spectra have been quantified [2.10]. In these examples the oxide films were only -5 nm thick on iron and -3 nm thick on the alloy. 

Wechsel-winkel, m.pl. alternate angles, -wir-kung, /. reciproc action or effect, -zahl, /. number of changes or alternations, cycle number, frequency, -zersetzung, /. double (or mutual) decomposition. 

There are certain histologic subtypes of diffuse, aggressive NHL that respond less well to treatment with conventional regimens such as CHOP. Burkitt s lymphoma, lymphoblastic lymphoma, mantel cell lymphoma, and primary CNS lymphoma are examples of disease that benefit from more intensive therapy. Regimens such as hyper-CVAD, which alternate cycles of hyperfractionated cyclophosphamide, doxorubicin, vincristine, and dexamethasone with high-dose cytarabine and methotrexate, often are substituted for CHOP. Intrathecal therapy with methotrexate is indicated with documented CNS infiltration of tumor or involvement of the sinuses. The recent appreciation of the etiology of Helicobacter pylori in the etiology of peptic ulcer disease and the association between colonization and mucosal-associated lymphoma (MALT) has spurred... 

Monitoring. The performance should be monitor to determine the number needed alternating cycles. 

Fig. 13.12 (a) Supported polymer MNF with two ends coupled to fiber tapers, (b) Time dependence of the MNF transmittance to alternately cycling air with 75% and 88% relative humidity, (c) Time dependence of the MNF absorbance to cyclic NO nitrogen exposure with N02 concentration from 0.1 to 4 ppm. Inset, dependence of the absorbance over the N02 concentration ranging from 0.1 to 4 ppm. Reprinted from Ref. 22 with permission. 2008 American Chemical Society... 

Whereas, from all of these informative 1H-PHIP-NMR spectra, the structure of the dihydride intermediate (including geometric details about peculiar bonding therein) can be determined rather exactly and reliably, a degree of uncertainty remains as to whether this intermediate represents the major or the minor diastereomer according to the nomenclature of Halpern [27]. This is the consequence of different kinetic constants associated with the two alternative cycles with different stereochemistry, and which accounts for the major and minor reaction product (Fig. 12.18). In fact, it is the difference in the rate... 

Iron objects which are exposed to the atmosphere or are partly immersed in water are often subjected to alternate cycles of wetting and drying (Pourbaix, 1974 Schwitter and Bdhni, 1980). These cycles may be due to seasonal fluctuations in weather conditions or be the result of tidal movements or of splashing. They cause the corro-... 

The maximum conversion of thymine to photoproducts in frozen aqueous solutions is 83-90%31 in samples subjected to alternate cycles of freezing and thawing, and 48-50% in samples continuously frozen during irradiation. This difference is attributed to depletion of thymine in the thymine crystallites of the continuously frozen solutions. The existence of a maximum at less than 100% in the conversion may reflect either the equilibrium always present between monomer and dimer, or... 

Figure 6. Solid-support-based protocol for the synthesis of a quadrilateral. Beginning with the support containing a closed junction, alternate cycles of restriction and ligation are performed, always at the position indicated as 1 . Selection of the target product (triangle, quadrilateral, pentalateral,...) is determined by the point at which one chooses to restrict at site 2, exposing a sticky end complementary to that exposed by restriction at site 1. This action corresponds to a strand switch (eliminating a zero node), of the sort shown in Figure 8, below. This is emphasized by the lines of different thickness with which the square catenane is drawn.

Scheme 3 forms a catalytic cycle for the water-gas shift reaction (63) employing [Rh2(/i-CO)(CO)2(dpm)2] in the presence of acid as a catalyst (62). It should be reiterated that alternative cycles might be written which do not involve formate intermediates. For example, a possible mechanism for catalysis of the water-gas shift reaction involving the binuclear metal species, [Pt2H2( -HXdpm)2]+, is outlined below (Scheme 4) (64). We have critically discussed the role of formate versus carboxylic acid intermediates in homogeneous catalysis of the water-gas shift reaction by mononuclear metal catalysts elsewhere (34).

Measured total sulfide levels confirm the major features of the hypotheses of Elliott and coworkers (8-11). in that sulfide seems to exist in remote oxic waters at concentrations approaching nanomolar, sufficient for meaningful metal interactions. The amplitude of the diurnal variation is too strong, however, for carbonyl sulfide hydrolysis to be the primary input, or for direct oxidation by O2 to be the sole sink, and alternate cycling processes are indicated. 

The French R D focuses on three baseline processes which require high temperatures high temperature steam electrolysis (HTSE), and the sulphur-iodine (S-I) and hybrid sulphur (HyS) thermochemical cycles. Alternative cycles able to operate at lower temperatures (Cu-Cl in particular) have also been investigated. All these cycles are being assessed from a feasibility point of view and some technical hurdles remain. Laboratory-scale experiments are ongoing and will give important... 

A series of UTC were investigated using a combination of thermodynamic analysis and experiments. The thermodynamics of alternative cycles were analysed using Outokumpu s HSC 5.0 Chemistry software computer code version 5.11 (Outokumpu, 2002). 

The Unmixed Reforming (UMR) process operates by alternately cycling between steam reforming and regeneration. The regeneration step provides the heat required by the endothermic steam reforming reactions utilizing a process known as Unmixed Combustion (UMC). 

A DC offset between the two channels is not eliminated by this cycle but is eliminated by a two-pulse cycle in which the phase of the transmitter is altered by 180° on successive acquisitions and the resulting signals are alternately added and subtracted. Because the desired Fourier-transformed signal changes sign while the DC offset does not, subtraction cancels the offset but causes all real signals to add. To cancel both channel imbalance and DC offsets simultaneously, we must nest our original two-pulse cycle in a two-pulse phase-alternated cycle to produce the four-step CYCLOPS cycle ... 

Fig. 8. Lifetime prediction using alternative cycle count...

When using a resin from new it is advisable to pre-condition the material by alternately cycling and rinsing the resin between acid and salt form (Na) for cation exchangers or hydroxide and salt form (Cl) for anion exchangers. This serves to osmotically cycle the resin and flush out residual impurities left over from the manufacturing process. 

---