A Note of Caution

Before becoming too enchanted by this vision, it is important to realize that the Hydrogen Economy is a complex concept that embraces a range of possibilities. Among the more important categories, it is therefore important to distinguish between  

Within these broad categories, there are numerous detailed production routes from primary energy sources (both fossil fuels and renewables) and manifold applications to be evaluated, each of which will impose its own individual technical and economic specifications. The role that hydrogen will play in future energy scenarios will only be known when all the remaining research and development has been completed, when demonstrations projects have been conducted and when full technical and economic evaluations have been made within the context of the prevailing energy scene at that time. 

Key World Energy Statistics, 2004 and 2006 Editions, International Energy Agency, Paris, 2004 and 2006. 

Collot, Prospects for Hydrogen from Coal, Report CCC/78, lEA Clean Coal Centre, London, December 2003. 

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However, a note of caution should be added. In many multiphase reaction systems, rates of mass transfer between different phases can be just as important or more important than reaction kinetics in determining the reactor volume. Mass transfer rates are generally higher in gas-phase than liquid-phase systems. In such situations, it is not so easy to judge whether gas or liquid phase is preferred. 

Organo-metallic compounds, on the other hand, behave very much like organic compounds, e.g. they can be redistilled and may be soluble in organic solvents. A note of caution should be made about handling organo-metallic compounds, e.g. arsines, because of their potential toxicities, particularly when they are volatile. Generally the suppliers of such compounds provide details about their safe manipulation. These should be read carefully and adhered to closely. If in any doubt always assume that the materials are lethal and treat them with utmost care. The same safety precautions about the handling of substances as stated in Chapter 4 should be followed here (see Chapter 1). 

A note of caution about roof fasteners. A common mistake is to fix a galvanised or aluminium roof in place with nails or screws of a different metal copper or brass, for instance. The copper acts as cathode, and the zinc or aluminium corrodes away rapidly near to the fastening. A similar sort of goof has been known to occur when copper roofing sheet has been secured with steel nails. As Fig. 24.6 shows, this sort of situation leads to catastrophically rapid corrosion not only because the iron is anodic, but because it is so easy for the electrons generated by the anodic corrosion to get away to the large copper cathode. 

These genetic experiments clearly demonstrated that the proposed structural model for the binding of these proteins to the phage operators was essentially correct. The second a helix in the helix-turn-helix motif is involved in recognizing operator sites as well as in the differential selection of operators by P22 Cro and repressor proteins. However, a note of caution is needed many other early models of DNA-protein interactions proved to be misleading, if not wrong. Modeling techniques are more sophisticated today but are still not infallible and are certainly not replacements for experimental determinations of structure. 

Most recent publications by Hartshorn and his collaborators introduce a note of caution with regard to the mechanistic interpretation of results obtained in BF3-catalyzed epoxide cleavage reactions. They point out the marked dependence of the course of the reaction on the solvent used, either... 

A note of caution on the use of photo-etched channels has been offered by RAMSHAWfl3 ) who points out that the system is attractive in principle provided that severe practical problems such as fouling are not encountered. With laminar flow in matrices with a mean plate spacing of 0.3-1 mm, volumetric heat transfer coefficients of 7 MW/m3 K have been obtained with modest pressure drops. Such values compare with 0.2 MW/m3 K for shell and tube exchangers and 1.2 MW/m3 K for plate heat exchangers. 

A note of caution is appropriate at this juncture as many confuse the inherent hazard of materials with risk. This will be covered in slightly greater detail later in this chapter, but it is important to distinguish between hazard and risk. Risk is defined as being a function of the inherent hazard of a material and the potential, or likelihood, for exposure ... 

A note of caution is necessary when we let MATLAB generate the state space model from a transfer function. The vector C (from S. c) is [0 0.5], which means that the indexing is reversed such that x2 is the output variable, and xl is the derivative of x2. Secondly, C is not [0 1], and hence we have to rescale the matrices B and C. These two points are further covered in MALTA Session 4. 

However, a note of caution should be added. In many multiphase reaction systems, as will be discussed in the next chapter, rates of mass transfer between different phases... 

It is appropriate to conclude our discussion of reaction mechanisms on a note of caution. A mechanism is merely a logical hypothesis as to... 

De la Fuente-Fernandez, R. A note of caution on correlation between sibling pairs. Neurology 60 1561,2003. 

Recently, the lateral pressure profile in a bilayer has been discussed in the context of partitioning of proteins in bilayers [100]. It is argued that this pressure profile can be used to rationalise the effects of additives on the membrane properties. Here a note of caution is necessary. It is not possible to define the lateral pressure profile through a bilayer unambiguously. The reason for this problem is that the local pressure not only has contributions that come from the local densities (this property is uniquely defined), but also from... 

A note of caution should be given here regarding the Hamiltonian matrix in Eq. [13]. It is not difficult to see that singularities can arise when the radial coordinates approach zero, which in turn could result in serious convergence... 

A note of caution should be sounded here. Whilst the curves shown in Figure 6.5 are characteristic of many charged dispersions it should be recalled that once we apply a sinusoid to a non-linear system the response need not be a sinusoid. As the strain is increased into the nonlinear region, the waveform passing through the sample becomes progressively distorted. The instrumental analysis in this case involves... 

This approach has been not only used to directly estimate the ocean pH from 8 B of foraminifera but to estimate from the pn the past atmospheric CO2 concentrations (i.e. Pearson and Palmer 1999,2000 Pagani et al. 2005). An increase in atmospheric CO2 results in increased dissolved CO2 in ocean water, which in turn causes a reduction in oceanic pn- A note of caution was presented by Lemarchand et al. (2000) who suggested that boron isotope variations in foraminifera depend at least in part on variations in the supply of riverine boron to the ocean during the geologic past. And indeed the boron isotope composition of rivers can be extremely variable (Rose et al. 2000 Lemarchand et al. 2002). Joachimski et al. (2005) presented evidence... 

A note of caution must be sounded with regard to the absolute values of therapeutic or toxic blood phenytoin levels, for these may differ markedly depending on the method and place of assay. A recent survey revealed large variations between results obtained by several laboratories, which on occasions, were as great between those employing the same type of analytical process (for example GLC) as between laboratories using other techniques. 

These are the modern active databases that have interactive capabilities, and are often searchable for a set of properties. The floppy disks and CD-ROMs have definite dates on them, and do become obsolete with time the Internet databases can, in principle, be updated at very frequent intervals. A note of caution about Internet databases is that some of them have not been vetted for accuracy and can be unreliable. 

A note of caution is necessary for companies seeking to enter contract research in Western countries and Japan. Because of the low salaries of Chinese and Indian scientists and their longer work hours, the cost advantage of Asian competitors is even more dramatic than in other segments of the hne-chemical industry. Whereas the prime cost of Indian custom manufacturers is about 40% of their Western competitors, it is only 20% for contract research Attracted by FTEs of 60,000 in the East versus 200,000 in the West, big pharma in particular is gravitating to these firms at the expense of their traditional USA- and EU-based CROs. 

Class 2A and 2B animal carcinogens and probable and possible human carcinogens, respectively. A note of caution is appropriate, however, regarding differences in the classification schemes. For example, the EPA classifications for BaP and BbF are both B2, sufficient evidence from animal studies. ... 

A note of caution is necessary when deahng with these materials. It is not trivial to distinguish between CuInS(Se)2 and some phases of Cu—S(Se). Diffraction and optical properties may be similar. Elemental analysis is particularly important to verify inclusion of indium in the films and in the correct ratio. A fingerprint of the chalcopyrite XRD is the presence of a weak peak at 26 = 17-18°, corresponding to the (101) chalcopyrite reflection. This is often not seen, although this could be either because the deposit is not chalcopyrite or because weak peaks are usually not seen in nanocrystaUine materials with particularly small crystal size. 

Chamomile (Matricaria camomilla) The flowers of this plant are dried and crushed into a tea, and people who drink chamomile tea half an hour or so before bedtime report getting a restful night s sleep. Chamomile tea can be useful for mild insomnia that occurs occasionally. Chamomile contains molecules called flavonoids, particularly chrysin, that calm the activity of nerve cells, although it is unknown exactly how this is achieved. Chamomile can also help relieve anxiety. A note of caution Since chamomile is a plant... 

Siebert, D.J. (1994b). Salvinorin A Notes of Caution. The Entheogen Review 3 (4) 2-3. 

Boosting Salvia with MAPI s Salvinorin A A Note of Caution by Daniel Siebert... 

A note of caution is needed here. The figures of merit presented in this section refer to the multivariate calibration model. This multivariate model, built with standards, is then applied to future real samples. If standards and real samples match, as should be the case in most applications, the calibration model is the essential step of the overall analytical procedure. However, if real samples require additional steps (basically preprocessing steps such as extractions, preconcentrations, etc.) different from those of the standards, then the calibration model is just one more step in the whole procedure. If the previous steps are not the same, this means that the figures of merit calculated for the model do not refer to the whole analytical procedure and, therefore, other approaches should be undertaken to calculate them [56]. 

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