Modelling and Multi-stage Design of Membrane Processes Applied to Carbon Capture in Coal-fired Power Plants

AbstractAccording to recent predictions, energy generation from coal will continue to play a key role in the next decades. The UK 2008 Climate Change Act requires a reduction of 80% of greenhouse gases emissions by 2050, and carbon capture and storage will have a key role in order to meet this target.This work focuses on post-combustion capture from coal-fired power plants based on membrane separation. Adetailed multi-stage design is presented: the developed flowsheet includes cross-flow and countercurrent-sweep stages. The cross-flow stages are based on a 2D model implemented by our research group able to predict the separation through spiral-wound permeators. Different process configurations are analysed, with the aim of reducing both energy consumption and membrane area.An economic analysis is also included: both capture and avoidance costs are evaluated. The estimated values are compared with data available in the literature for processes based on amine capture technology

Optimal Dynamic Procurement Policies for a Storable Commodity with L\'evy Prices and Convex Holding Costs

In this paper we study a continuous time stochastic inventory model for a commodity traded in the spot market and whose supply purchase is affected by price and demand uncertainty. A firm aims at meeting a random demand of the commodity at a random time by maximizing total expected profits. We model the firm's optimal procurement problem as a singular stochastic control problem in which controls are nondecreasing processes and represent the cumulative investment made by the firm in the spot market (a so-called stochastic "monotone follower problem"). We assume a general exponential L\'evy process for the commodity's spot price, rather than the commonly used geometric Brownian motion, and general convex holding costs. We obtain necessary and sufficient first order conditions for optimality and we provide the optimal procurement policy in terms of a "base inventory" process; that is, a minimal time-dependent desirable inventory level that the firm's manager must reach at any time. In particular, in the case of linear holding costs and exponentially distributed demand, we are also able to obtain the explicit analytic form of the optimal policy and a probabilistic representation of the optimal revenue. The paper is completed by some computer drawings of the optimal inventory when spot prices are given by a geometric Brownian motion and by an exponential jump-diffusion process. In the first case we also make a numerical comparison between the value function and the revenue associated to the classical static "newsvendor" strategy.Comment: 28 pages, 3 figures; improved presentation, added new results and section

Generalized Kuhn-Tucker Conditions for N-Firm Stochastic Irreversible Investment under Limited Resources

In this paper we study a continuous time, optimal stochastic investment problem under limited resources in a market with N firms. The investment processes are subject to a time-dependent stochastic constraint. Rather than using a dynamic programming approach, we exploit the concavity of the profit functional to derive some necessary and sufficient first order conditions for the corresponding Social Planner optimal policy. Our conditions are a stochastic infinite-dimensional generalization of the Kuhn-Tucker Theorem. The Lagrange multiplier takes the form of a nonnegative optional random measure on [0,T] which is flat off the set of times for which the constraint is binding, i.e. when all the fuel is spent. As a subproduct we obtain an enlightening interpretation of the first order conditions for a single firm in Bank (2005). In the infinite-horizon case, with operating profit functions of Cobb-Douglas type, our method allows the explicit calculation of the optimal policy in terms of the `base capacity' process, i.e. the unique solution of the Bank and El Karoui representation problem (2004).Comment: 25 page

A generalization of the "probléme des rencontres"

In this paper, we study a generalization of the classical \emph{probl\'eme des rencontres} (\emph{problem of coincidences}), consisting in the enumeration of all permutations \pi \in \SS_n with $k$ fixed points, and, in particular, in the enumeration of all permutations \pi \in \SS_n with no fixed points (derangements). Specifically, we study this problem for the permutations of the $n+m$ symbols $1$, $2$, \ldots, $n$, $v_1$, $v_2$, \ldots, $v_m$, where $v_i \not\in\{1,2,\ldots,n\}$ for every $i=1,2,\ldots,m$. In this way, we obtain a generalization of the derangement numbers, the rencontres numbers and the rencontres polynomials. For these numbers and polynomials, we obtain the exponential generating series, some recurrences and representations, and several combinatorial identities. Moreover, we obtain the expectation and the variance of the number of fixed points in a random permutation of the considered kind. Finally, we obtain some asymptotic formulas for the generalized rencontres numbers and the generalized derangement numbers

The interaction of the alpha-2 chimaerin SH2 domain with target proteins

Rac is a member of the Rho subfamily of low molecular weight GTPases (p21s) and is involved in diverse cellular processes. GTPase-activating proteins (GAPs) regulate p21 activity by increasing intrinsic GTPase activity. The chimaerins are a family of p21-Rac GAPS with distinct patterns of tissue and developmental distribution, α2 chimaerin contains an amino-terminal SH2 domain and is selectively expressed within the nervous system. SH2 domains bind specific phosphotyrosine-containing sequences and the presence of this domain may place α2 chimaerin within tyrosine kinase signalling pathways. Comparisons between SH2 domains suggest that the mechanism of target interaction of the chimaerin SH2 domain may be distinct from that of others. Affinity chromatography was used to detect potential α2 chimaerin SH2 domain target proteins in rat brain extracts; some of these proteins were tyrosine-phosphorylated. Tubulin and actin were isolated as targets and peptide sequence information was obtained for three other potential target proteins, two of which appeared to be novel sequences. Several different kinase activities bound α2 chimaerin SH2 domain affinity columns; one of these phosphorylated full length α2 chimaerin. Full length α2 chimaerin and its isolated SH2 domain bound a phosphotyrosine column. Amino acid residue substitutions were made in the α2 chimaerin SH2 domain at sites essential for function in other SH2 domains; certain point mutations affected phosphotyrosine-binding. α2 Chimaerin probes bound two previously identified putative α2 chimaerin target proteins of molecular mass 13kDa and 64kDa; these interactions were phosphotyrosine-independent. The interactions of the 13kDa and 64kDa proteins with α2 chimaerin differed in their sensitivity to point mutation of the chimaerin SH2 domain. Specific antibodies have been raised to these proteins to facilitate further studies. Results suggest that substrates of the α2 chimaerin SH2 domain may include both tyrosine-phosphorylated and non-tyrosine phosphorylated proteins

The String Tension in Gauge Theories: a Suggestion for a New Measurement Method

We discuss a new method for testing confinement and measuring the string tension (in the Coulomb gauge). Our numerical simulations demonstrate that the problems related to Gribov copies are not harmful and that the method is effective in the case of pure gauge Q.C.D.. We discuss the relevance of the method for studying gauge theories coupled to fermionic matter.Comment: 9 pages, Latex style, 4 postscript figures appended, ROMA 92-90

Insertions Yielding Equivalent Double Occurrence Words

A double occurrence word (DOW) is a word in which every symbol appears exactly twice; two DOWs are equivalent if one is a symbol-to-symbol image of the other. We consider the so called repeat pattern ($\alpha\alpha$) and the return pattern ($\alpha\alpha^R$), with gaps allowed between the $\alpha$'s. These patterns generalize square and palindromic factors of DOWs, respectively. We introduce a notion of inserting repeat/return words into DOWs and study how two distinct insertions into the same word can produce equivalent DOWs. Given a DOW $w$, we characterize the structure of $w$ which allows two distinct insertions to yield equivalent DOWs. This characterization depends on the locations of the insertions and on the length of the inserted repeat/return words and implies that when one inserted word is a repeat word and the other is a return word, then both words must be trivial (i.e., have only one symbol). The characterization also introduces a method to generate families of words recursively

The Rare Book Collection of the Library of the Italian National Institute of Health: from the past to the present

The Library of the Istituto Superiore di Sanità (ISS), the Italian National Institute of Health, is the main library for public health and biomedical research in Italy and holds a small but valuable special collection of ancient books. Known as the Rare Book Collection, this fund consists of over 1200 scientific printed volumes published between the XVI and the XIX century. The purpose of this paper is to illustrate the challenges and the process undertaken by the Library to share and digitalize this Collection