Solutions diversification in a column generation algorithm

International audienceColumn generation algorithms have been specially designed for solving mathematical programs with a huge number of variables. Unfortunately, this method suffers from slow convergence that limits its efficiency and usability. Several accelerating approaches are proposed in the literature such as stabilization-based techniques. A more classical approach, known as "intensification, consists in inserting a set of columns instead of only the best one. Unfortunately, this intensication typically overloads the master problem, and generates a huge number of useless variables. This article covers some characteristics of the generated columns from theoretical and experimental points of view. Two selection criteria are compared. The first one is based on column reduced cost and the second on column structure. We conclude our study with computational experiments on two kinds of problems: the acyclic vehicle routing problem with time windows and the one-dimensional cutting stock. problem

Enforcing International Law: Implications for an Effective Global Warming Regime

Syftet med denna studie var att undersöka den antibakteriella effekten hos ett polyestertyg med tunna invävda koppartrådar. Frågeställningen som skulle besvaras var ifall koppartyget hade en baktericid eller bakteristatisk effekt. Koppartyget är ännu i prototypstadie och om det visar sig ha antibakteriella egenskaper är det tänkt att användas inom klinisk verksamhet för att förhindra bakterietillväxt i sår och andra känsliga lokaler. Koppar är ett essentiellt spårämne, men har också antimikrobiella egenskaper som utövas genom ett brett spektra av mekanismer där skador på cellmembranet är en av de viktigare. Metoderna som användes för att inokulera bakterier på tyget var absorptionsmetoden, där en näringsbuljong innehållande Staphylococcus aureus ATCC 6538 pipetterades på tygproverna, och transfermetoden där tygproverna trycktes mot en agar som racklats med peptonsaltlösning innehållande S. aureus. Totalantalet viabla bakterier per tygprov beräknades efter kort kontakt (<1min) och inkubering (18-24 h vid 37±2°C) genom att räkna viable count. Resultaten efter inkubering visade signifikant skillnad i totalantal bakterier mellan koppartyget och negativ kontroll i tre av fyra försök. Kort kontakt visade tendens till viss antibakteriell effekt. Slutsatsen är att koppartyget skadade och dödade bakterier då de fick inkubera på tyget, medan fler försök behövs för att säkerställa effekten av kort kontakt med koppartyget. The purpose of this study was to test the antibacterial effect of thin copper treads woven into a polyester fabric. The investigation was done by inoculation of Staphylococcus aureus strain ATCC 6538 to the fabric and evaluation of the number of viable cells post exposure by viable count. The issue to be answered was whether the copper fabric had a bactericide or bacteriostatic effect? The fabric is still in prototype stage, and if proven to have antibacterial properties the aim is to use it to prevent bacterial growth in wounds and other vulnerable locations in clinical care. Copper is an essential trace element, but also has antimicrobial properties through a wide range of mechanisms where cell membrane damage is one of the more important. Methods used for inoculation was the absorption method, where a nutrient broth containing S. aureus was pipetted on to the fabric specimens, and the transfer method where the fabric specimens were pressed onto an agar plate that had previously been spread with peptone salt solution containing S. aureus. Total number of bacteria per fabric specimen after short contact (<1 min) and incubation (18-24 h at 37±2°C) was calculated. Incubation showed significant difference in total number of bacteria between the copper fabric and negative control in three of four tests. Short contact showed a tendency of antibacterial effect. The conclusion was that the copper fabric harmed and killed bacteria during incubation but that more records would be needed to be sure about the effects of short contact on bacteria

Reform of the Japanese Banking System

Japan has experienced a decade-long economic stagnation with a distressed banking sector in the 1990s. The absence of a credit culture to rigorously assess and price credit risks of borrowers, aggravated by weak prudential and supervisory frameworks, in the 1980s, the collapse of the asset price bubble in the early 1990s, and the lack of decisive, comprehensive strategy to address the banking sector problem at an early stage were largely responsible for the emergence of banking sector problems. All of these allowed a systemic banking crisis to emerge in 1997-98 and a large output loss during 1998-2002. The crisis ultimately prompted the government to take a more aggressive policy to tackle the problem. Sufficient progress has been made since then on banking sector stabilization, restructuring, and consolidation. The regulatory and supervisory framework has been strengthened in a way consistent with an increasingly market-oriented, globalized environment. As a result, the worst is over in the Japanese banking system, setting the stage for sustained economic recovery. Though bank capital may still be inadequate, safety nets are in place, the credit allocation has been made more rational. Remaining risks are limited to regional and smaller institutions that are vulnerable to weak, local economic conditions and hikes of the long-term interest rate.Asset price bubble, Japan's "lost decade", systemic banking sector crisis, bank restructuring and consolidation, market-based regulatory and supervisory framework

Reformulation and decomposition of integer programs

In this survey we examine ways to reformulate integer and mixed integer programs. Typically, but not exclusively, one reformulates so as to obtain stronger linear programming relaxations, and hence better bounds for use in a branch-and-bound based algorithm. First we cover in detail reformulations based on decomposition, such as Lagrangean relaxation, Dantzig-Wolfe column generation and the resulting branch-and-price algorithms. This is followed by an examination of Benders’ type algorithms based on projection. Finally we discuss in detail extended formulations involving additional variables that are based on problem structure. These can often be used to provide strengthened a priori formulations. Reformulations obtained by adding cutting planes in the original variables are not treated here.Integer program, Lagrangean relaxation, column generation, branch-and-price, extended formulation, Benders' algorithm

Anglo-American corporate governance and the employment relationship: a case to answer

The corporate governance environment in the UK and US is generally thought to be hostile to the emergence of cooperative employment relations of the kind exemplified by labour-management partnerships. We discuss case study evidence from the UK which suggests that, contrary to this widespread perception, enduring and proactive partnerships may develop, in conditions where management can convince shareholders of the long-term gains from this approach, and where other regulatory factors operate to extend the time-horizon for financial returns. We conclude that there is more scope than is commonly allowed for measures which could reconcile liquidity in capital markets with cooperation in labour relations

Bretton Woods and the U.S. decision to intervene in the foreign-exchange market, 1957-1962

The deterioration in the U.S. balance of payments after 1957 and an accelerating loss of gold reserves prompted U.S. monetary authorities to undertake foreign-exchange-market interventions beginning in 1961. We discuss the events leading up to these interventions, the institutional arrangements developed for that purpose, and the controversies that ensued. Although these interventions forestalled a loss of U.S. gold reserves, in the end, they only delayed more fundamental adjustments and, in that respect, were a failure.Foreign exchange administration ; Bretton Woods Agreements Act

The effectiveness of monetary policy

The analysis addresses changing views of the role and effectiveness of monetary policy, inflation targeting as an "effective monetary policy," monetary policy and short-run (output) stabilization, and problems in implementing a short-run stabilization policy.Monetary policy