Root numbers and ranks in positive characteristic

For a global field K and an elliptic curve E_eta over K(T), Silverman's specialization theorem implies that rank(E_eta(K(T))) <= rank(E_t(K)) for all but finitely many t in P^1(K). If this inequality is strict for all but finitely many t, the elliptic curve E_eta is said to have elevated rank. All known examples of elevated rank for K=Q rest on the parity conjecture for elliptic curves over Q, and the examples are all isotrivial. Some additional standard conjectures over Q imply that there does not exist a non-isotrivial elliptic curve over Q(T) with elevated rank. In positive characteristic, an analogue of one of these additional conjectures is false. Inspired by this, for the rational function field K = kappa(u) over any finite field kappa with odd characteristic, we construct an explicit 2-parameter family E_{c,d} of non-isotrivial elliptic curves over K(T) (depending on arbitrary c, d in kappa^*) such that, under the parity conjecture, each E_{c,d} has elevated rank.Comment: 40 pages; last version; to appear in Adv. Mat

A tale of pork prices : evasion and attenuation of a Japanese tariff

This paper empirically examines the effectiveness of a safeguard tariff in the Japanese market for imported pork parts. The goals are, first, to consider a refinement to the traditional market-based method for evasion detection, and, second, to apply the method in a setting where evasion is suspected to be widespread. Utilising a within-pig variation in tariff burdens and the timing of safeguard invocations, I examine a panel of monthly wholesale prices on narrowly-defined pork products from 2001 through 2008. The results are consistent with a hypothesis that a widespread evasion nullified the safeguard tariff on pork, and are robust to a range of alternative explanations including the adjustment of profit margins by traders. Safeguard tariffs appear to be a simple mechanism, but behavioural responses can undo the policy intent.safeguard tariff, price disparity, tax incidence

Public debt sustainability. An empirical study on OECD countries

For a panel of 21 OECD heterogeneous countries from 1991 to 2015, we study governments’ reactions to the accumulation of debt and look at whether governments voluntary take corrective measures when the debt-GDP ratio starts rising or they rather let the debt grow. We distinguish between discretionary and automatic response of primary balance of government actions, as captured by the structural component of public primary balance and by cyclical component of public primary balance. We show the existence of a systematic long-term relationship between debt and structural primary balance supporting the view that the long-term governments’ discretionary response to increases in the debt-GDP ratio is negative, that is, governments are not currently taking long-term actions that counteract the increases in debts and do not satisfy the intertemporal budget constraint. In the short term, an asymmetric fiscal policy response exploiting the output gap, by part of the political class of the countries considered, seems to emerge: it intervenes with a new deficit and debt when the output gap is positive, but it does not adopt a symmetrical correction when the situation is reversed

An analysis of involuntary excess reserves, monetary policy and risk-taking behaviour of Chinese banks

In this paper, we examine the effects of monetary policy on the risk-taking behaviour of Chinese banks in the presence of involuntary excess reserves based on a sample of 95 banks. We find that involuntary excess reserves lead to more aggressive risk-taking suggesting that large involuntary excess reserves stimulate the rapid expansion of credit and the price bubble in the Chinese financial market. However, banks with larger involuntary excess reserves tend to reduce risk-taking more rapidly under the tightening monetary policy regime. The paper sheds light on the effectiveness of government monetary policy in reducing the risk-taking behaviour of banks in an emerging market where involuntary excess reserves are present

Hyperosmotic priming of arabidopsis seedlings establishes a long-term somatic memory accompanied by specific changes of the epigenome

&lt;p&gt;Background: In arid and semi-arid environments, drought and soil salinity usually occur at the beginning and end of a plant's life cycle, offering a natural opportunity for the priming of young plants to enhance stress tolerance in mature plants. Chromatin marks, such as histone modifications, provide a potential molecular mechanism for priming plants to environmental stresses, but whether transient exposure of seedlings to hyperosmotic stress leads to chromatin changes that are maintained throughout vegetative growth remains unclear.&lt;/p&gt; &lt;p&gt;Results: We have established an effective protocol for hyperosmotic priming in the model plant Arabidopsis, which includes a transient mild salt treatment of seedlings followed by an extensive period of growth in control conditions. Primed plants are identical to non-primed plants in growth and development, yet they display reduced salt uptake and enhanced drought tolerance after a second stress exposure. ChIP-seq analysis of four histone modifications revealed that the priming treatment altered the epigenomic landscape; the changes were small but they were specific for the treated tissue, varied in number and direction depending on the modification, and preferentially targeted transcription factors. Notably, priming leads to shortening and fractionation of H3K27me3 islands. This effect fades over time, but is still apparent after a ten day growth period in control conditions. Several genes with priming-induced differences in H3K27me3 showed altered transcriptional responsiveness to the second stress treatment.&lt;/p&gt; &lt;p&gt;Conclusion: Experience of transient hyperosmotic stress by young plants is stored in a long-term somatic memory comprising differences of chromatin status, transcriptional responsiveness and whole plant physiology.&lt;/p&gt

The Causal Relationship between Private and Public Investment in Zimbabwe

The study examines the relationship between private and public investment in Zimbabwe utilizing yearly time series data for the period 1970 to 2007. Emphasis is placed on the direction of causality and the effect of the two types of investment on each other. The paper constructs empirical models for both private and public investment, based on the flexible accelerator theory. Private investment is found to be cointegrated with public investment. A cointergration approach and VEC model are employed to assess the short run relationship existing between public and private investment. The relationship between private and public investment is found to be insignificant and the direction of causality found to be unidirectional. The results support the notion that private investment precedes public investment.Private Investment, Public Investment, Causality, Flexible Accelerator Theory, Zimbabwe