Analysis of Linsker's simulations of Hebbian rules

Linsker has reported the development of center-surround receptive fields and oriented receptive fields in simulations of a Hebb-type equation in a linear network. The dynamics of the learning rule are analyzed in terms of the eigenvectors of the covariance matrix of cell activities. Analytic and computational results for Linsker's covariance matrices, and some general theorems, lead to an explanation of the emergence of center-surround and certain oriented structures. We estimate criteria for the parameter regime in which center-surround structures emerge

The Role of Constraints in Hebbian Learning

Models of unsupervised, correlation-based (Hebbian) synaptic plasticity are typically unstable: either all synapses grow until each reaches the maximum allowed strength, or all synapses decay to zero strength. A common method of avoiding these outcomes is to use a constraint that conserves or limits the total synaptic strength over a cell. We study the dynamic effects of such constraints. Two methods of enforcing a constraint are distinguished, multiplicative and subtractive. For otherwise linear learning rules, multiplicative enforcement of a constraint results in dynamics that converge to the principal eigenvector of the operator determining unconstrained synaptic development. Subtractive enforcement, in contrast, typically leads to a final state in which almost all synaptic strengths reach either the maximum or minimum allowed value. This final state is often dominated by weight configurations other than the principal eigenvector of the unconstrained operator. Multiplicative enforcement yields a “graded” receptive field in which most mutually correlated inputs are represented, whereas subtractive enforcement yields a receptive field that is “sharpened” to a subset of maximally correlated inputs. If two equivalent input populations (e.g., two eyes) innervate a common target, multiplicative enforcement prevents their segregation (ocular dominance segregation) when the two populations are weakly correlated; whereas subtractive enforcement allows segregation under these circumstances. These results may be used to understand constraints both over output cells and over input cells. A variety of rules that can implement constrained dynamics are discussed

Facets of sovereignty. Institutions that Spur and Institutions that Retard Tribal Development.

That so many of their assets continue to be held in governmental trusts under outdated policy rationales creates great difficulty for indigenous peoples. But restoring control of those assets to their rightful owners will impose daunting responsibilities on judiciaries. Exchanging assets for a residual share of returns from a joint venture exposes one to shirking by co-investors. Judiciaries known reliably to penalize those who renege on commitments help investors persuade others to sink complementary assets in promising projects. But a court is an arm of the sovereign. Across history and geography justifiable rulings adverse to sovereigns have so often been honored in the breach that private parties are especially leery of sovereigns as co-investors. To attract assets into its realm a sovereign may thus invest in a reputation for abiding by waivers of sovereign immunity, or rely on a still stronger sovereign to bond its waivers. Reputations arise from observed court successes by aggrieved co-investors when their suits against the sovereign are meritorious. But many tribal reservations are small and poor, have offered few investment opportunities, and hence possess thin legal histories. At the same time, investors are skeptical that courts of more powerful sovereigns such as Canada and the United States dependably bond tribal waivers. Thus tribes often must pay investors high risk-premiums, resort to costly tribal ownership, or even forego promising opportunities altogether. The Sovereign’s Paradox refers to the difficulty that an entity with power to compel involuntary outcomes has in negotiating voluntary ones. This chapter explores ways to ameliorate that Paradox and thus improve returns from reservation assets.

Introduction to the themed issue - Corporate power : agency, communication, influence and social policy

This paper introduces this themed issue of Critical Social Policy on the question of corporate power. Corporate power is recognized as an important agent in social policy making and delivery. However, to date there has been comparatively little attention to the crucial role that lobbying and corporate 'spin' play in helping to shape policy making contexts. This special issue of Critical Social Policy is concerned to bring such issues to the mainstream of social policy analysis. It is argued here that the rise of spin and public relations is a key feature of neoliberalism in the past two decades. These have worked to reshape policy making, resulting in pronounced changes in the content and process of policy making and it is argued that these have tended to marginalize or undermine democratic processes

Boosting Higgs CP properties via VH Production at the Large Hadron Collider

We consider ZH and WH production at the Large Hadron Collider, where the Higgs decays to a bb pair. We use jet substructure techniques to reconstruct the Higgs boson and construct angular observables involving leptonic decay products of the vector bosons. These efficiently discriminate between the tensor structure of the HVV vertex expected in the Standard Model and that arising from possible new physics, as quantified by higher dimensional operators. This can then be used to examine the CP nature of the Higgs as well as CP mixing effects in the HZZ and HWW vertices separately.Comment: 5 pages, 3 figures. v2: two references added and typo correcte

No well-defined remnant Fermi surface in Sr2CuO2Cl2

In angle-resolved photoelectron spectra of the antiferromagnetic insulators Ca2CuO2Cl2 and Sr2CuO2Cl2 a sharp drop of the spectral intensity of the lowest-lying band is observed along a line in k space equivalent to the Fermi surface of the optimally doped high-temperature superconductors. This was interpreted as a signature of the existence of a remnant Fermi surface in the insulating phase of the high-temperature superconductors. In this paper it is shown that the drop of the spectral intensity is not related to the spectral function but is a consequence of the electron-photon matrix elementComment: 4 pages, 3 figure