Stiffness of finite free resolutions and the Canonical Element Conjecture

Over a noetherian local ring certain minimal finite free resolutions possess a property which we call stiffness. This calls to mind the Buchsbaum-Eisenbud criterion for exactness. Yet we only prove stiffness over equicharacteristic rings. However, Hochster's Canonical Element Conjecture is shown to be true for every ring with a fixed prime residual characteristic, precisely when every resolution over each Gorenstein ring of this type is stiff.Comment: 11 page

Using the Sun to estimate Earth-like planets detection capabilities. V. Parameterizing the impact of solar activity components on radial velocities

Stellar activity induced by active structures (eg, spots, faculae) is known to strongly impact the radial velocity time series. It then limits the detection of small planetary RV signals (eg, an Earth-mass planet in the habitable zone of a solar-like star). In previous papers, we studied the detectability of such planets around the Sun seen as an edge-on star. For that purpose, we computed the RV and photometric variations induced by solar magnetic activity, using all active structures observed over one entire cycle. Our goal is to perform similar studies on stars with different physical and geometrical properties. As a first step, we focus on Sun-like stars seen with various inclinations, and on estimating detection capabilities with forthcoming instruments. To do so, we first parameterize the solar active structures with the most realistic pattern so as to obtain results consistent with the observed ones. We simulate the growth, evolution and decay of solar spots, faculae and network, using parameters and empiric laws derived from solar observations and literature. We generate the corresponding structure lists over a full solar cycle. We then build the resulting spectra and deduce the RV and photometric variations for a `Sun' seen with various inclinations. The produced RV signal takes into account the photometric contribution of structures as well as the attenuation of the convective blueshift. The comparison between our simulated activity pattern and the observed one validates our model. We show that the inclination of the stellar rotation axis has a significant impact on the time series. RV long-term amplitudes as well as short-term jitters are significantly reduced when going from edge-on to pole-on configurations. Assuming spin-orbit alignment, the optimal configuration for planet detection is an inclined star (i~45{\deg}).Comment: Accepted to Astronomy and Astrophysics on May, 27th 2015. The manuscript includes 22 pages, 20 figure

Extrasolar planets and brown dwarfs around AF-type stars. IX. The HARPS southern sample

Massive, Main-Sequence AF-type stars have so far remained unexplored in past radial velocity surveys, due to their small number of spectral lines and their high rotational velocities that prevent the classic RV computation method. Our aim was to search for giant planets around AF MS stars, to get first statistical information on their occurrence rate and to compare the results with evolved stars and lower-mass MS stars. We used the HARPS spectrograph located on the 3.6m telescope at ESO La Silla Observatory to observe 108 AF MS stars with B-V in the -0.04 to 0.58 range and masses in the range 1.1-3.6 Msun. We used our SAFIR software specifically developed to compute the radial velocities of these early-type stars. We report the new detection of a mpsini = 4.51 Mjup companion with a ~826-day period to the F6V dwarf HD111998. We present new data on the 2-planet system around the F6IV-V dwarf HD60532. We also report the detection of 14 binaries with long-term RV trends. 70% of our targets show detection limits between 0.1 and 10 Mjup in the 1 to 10^3-day range. We derive brown dwarf (13 < mpsini < 80 Mjup) occurrence rates in the 1 to 10^3-day range of $2_{-2}^{+5}$% and $2.6_{-2.6}^{+6.7}$% for stars with masses in the ranges 1.1-1.5 and 1.5-3 Msun, respectively. As for Jupiter-mass companions (1 < mpsini < 13 Mjup), we get occurrence rates in the 1 to 10^3-day range of $4_{-0.9}^{+5.9}$% and $6.3_{-6.3}^{+15.9}$% respectively for the same stellar mass ranges. When considering the same Jupiter-mass companions but periods in the 1 to 100-day range only, we get occurrence rates of $2_{-2}^{+5.2}$% and $3.9_{-3.9}^{+9.9}$%. Given the present error bars, these results do not show a significant difference with companion frequencies derived for solar-like stars.Comment: 23 pages (text), 15 figures, accepted in Astronomy and Astrophysic

Torsion of injective modules and weakly pro-regular sequences

Let $R$ a commutative ring, $\mathfrak{a} \subset R$ an ideal, $I$ an injective $R$-module and $S \subset R$ a multiplicatively closed set. When $R$ is Noetherian it is well-known that the $\mathfrak{a}$-torsion sub-module $\Gamma_{\mathfrak{a}}(I)$, the factor module $I/\Gamma_{\mathfrak{a}}(I)$ and the localization $I_S$ are again injective $R$-modules. We investigate these properties in the case of a commutative ring $R$ by means of a notion of relatively-$\mathfrak{a}$-injective $R$-modules. In particular we get another characterization of weakly pro-regular sequences in terms of relatively injective modules. Also we present examples of non-Noetherian commutative rings $R$ and injective $R$-modules for which the previous properties do not hold. Moreover, under some weak pro-regularity conditions we obtain results of Mayer-Vietoris type.Comment: 14 pages, to appear in Comm. in Algebr

Dynamic pricing with demand learning under competition

Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 199-204).In this thesis, we focus on oligopolistic markets for a single perishable product, where firms compete by setting prices (Bertrand competition) or by allocating quantities (Cournot competition) dynamically over a finite selling horizon. The price-demand relationship is modeled as a parametric function, whose parameters are unknown, but learned through a data driven approach. The market can be either in disequilibrium or in equilibrium. In disequilibrium, we consider simultaneously two forms of learning for the firm: (i) learning of its optimal pricing (resp. allocation) strategy, given its belief regarding its competitors' strategy; (ii) learning the parameters in the price-demand relationship. In equilibrium, each firm seeks to learn the parameters in the price-demand relationship for itself and its competitors, given that prices (resp. quantities) are in equilibrium. In this thesis, we first study the dynamic pricing (resp. allocation) problem when the parameters in the price-demand relationship are known. We then address the dynamic pricing (resp. allocation) problem with learning of the parameters in the price-demand relationship. We show that the problem can be formulated as a bilevel program in disequilibrium and as a Mathematical Program with Equilibrium Constraints (MPECs) in equilibrium. Using results from variational inequalities, bilevel programming and MPECs, we prove that learning the optimal strategies as well as the parameters, is achieved. Furthermore, we design a solution method for efficiently solving the problem. We prove convergence of this method analytically and discuss various insights through a computational study.(cont.) Finally, we consider closed-loop strategies in a duopoly market when demand is stochastic. Unlike open-loop policies (such policies are computed once and for all at the beginning of the time horizon), closed loop policies are computed at each time period, so that the firm can take advantage of having observed the past random disturbances in the market. In a closed-loop setting, subgame perfect equilibrium is the relevant notion of equilibrium. We investigate the existence and uniqueness of a subgame perfect equilibrium strategy, as well as approximations of the problem in order to be able to compute such policies more efficiently.by Carine Simon.Ph.D

Un MOOC et ses partenaires - Remettre l'humain dans le massif

International audienceCes derniers mois, les MOOC ont attiré l'attention des professionnels de l'enseignement et la formation. Alors que la croissance des MOOC est phénoménale, des nombreuses critiques surgissent à propos des modèles économiques, l'ingénierie pédagogique insuffisante ou les taux d'abandon élevés. Du 10 octobre au 12 décembre 2013, la deuxième saison d'ITyPA a réuni quelques 2.600 participants. En collaboration avec une quarantaine de partenaires français et internationaux, des rencontres physiques et virtuelles étaient proposées afin de permettre aux inscrits de mieux appréhender les différents aspects du cours, de rythmer leur participation et de maintenir leur niveau de motivation. Du simple meet-up au programme de formation parallèle, les partenaires ont permis une plus grande personnalisation de l'expérience de l'apprenant dans le MOOC, un renforcement de l'ingénierie pédagogique et l'émergence de nouveaux modèles économiques

Equivocation and doublespeak in far right-wing discourse : an analysis of Nick Griffin’s performance on BBC’s Question Time

An analysis was conducted of the discourse of Nick Griffin (leader of the BNP, the far right-wing British National Party), as featured on a television debate, broadcast on the popular BBC current affairs program Question Time (22 October 2009). On the basis of equivocation theory (Bavelas et al. 1990), it was hypothesized that Griffin’s discourse may be seen to reflect an underlying communicative conflict. On the one hand, to be seen as racist is widely regarded as reprehensible in contemporary British society; on the other hand, much of the BNP’s political support comes from its anti-immigrant stance. In this context, it was proposed that while Griffin denies criticisms that characterize the BNP as anti-immigrant or racist, he puts over his political message through implicit meanings, seemingly vague and ambiguous, but which carry clear implications regarding the BNP’s continued underlying anti-immigrant stance. These implicit messages were further conceptualized as a form of “doublespeak” – language that deliberately disguises, distorts, or reverses the meaning of words, and which may be characterized as a form of “calculated ambivalence.

The origins of American international retailing:Tiffany of New York in London and Paris, 1837-1914

This article considers the international retailing activities of Tiffany of New York between 1837 and 1914. Using data from the company archive alongside other sources, the article considers the firm’s international retail operation from entry stage merchant buying activity through to the establishment of modern retailing facilities. The findings indicate five factors were determinants of sustainable international retailing: a centralized organizational structure, a stable ownership structure, existing international engagement, a strong brand identity, and a relevant international retail format. Placing Tiffany’s activities in its wider commercial and consumer context, the findings illustrate the organizational changes and asset combination required to support the development of early international retail operations. The article contributes to theoretical understanding of the dynamics of retail internationalization

Marketing Innovation in Time and across Time:International Flagship Stores, Brand Identity and the Boundary of the Firm

In this paper we problematize the contextualization and analysis of innovative international retailing practices in time and across time. Theoretically, the paper contributes to an understanding of the role of marketing activities in defining the boundary of the international retail firm. Using historical methods and drawing on primary data from firm-based archives in the United States and the United Kingdom this paper shows how adopting a long-term perspective on retail marketing innovation facilitates a deeper and richer understanding of the internationalization of retail activity from the perspective of practice and theory. We explore the epistemological challenges of incorporating historical methods into mainstream marketing research. These historiographical and theoretical issues are explored through consideration of the role of ‘flagship’ stores in the creation of brand identity in international markets during and between the first and second global economies: 1880 - 2019. Analyzing the experiences of American and British firms, this paper explores strategic tensions created by the relative financial and marketing value of iconic stores in prestigious locations in international markets. At the firm-level, the paper provides insight into the emergence and development of in-house branding, retailing and marketing practices. At the market-level, we explore how marketing innovation defined by the first global economy (1880-29) was challenged by volatile trading conditions after 1929 and subsequently reasserted in the late twentieth century and early twenty-first century (1980-2019)