Scalable Divisible E-cash

Divisible E-cash has been introduced twenty years ago but no construction is both fully secure in the standard model and efficiently scalable. In this paper, we fill this gap by providing an anonymous divisible E-cash construction with constant-time withdrawal and spending protocols. Moreover, the deposit protocol is constant-time for the merchant, whatever the spent value is. It just has to compute and store $2^l$ serial numbers when a value $2^l$ is deposited, compared to $2^n$ serial numbers whatever the spent amount (where $2^n$ is the global value of the coin) in the recent state-of-the-art paper. This makes a very huge difference when coins are spent many times. Our approach follows the classical tree representation for the divisible coin. However we manage to build the values on the nodes in such a way that the elements necessary to recover the serial numbers are common to all the nodes of the same level: this leads to strong unlinkability and anonymity, the strongest security level for divisible E-cash

The U-shaped Investment Curve: Theory and Evidence

This paper examines how the investment of financially constrained firms varies with their level of internal funds. We develop a theoretical model of optimal investment under financial constraints. Our model endogenizes the costs of external funds and allows for negative levels of internal funds. We show that the resulting relationship between internal funds and investment is U-shaped. In particular, when a firm's internal funds are negative and sufficiently low, a further decrease leads to an increase in investment. This effect is driven by the investor's participation constraint: when part of any loan must be used to close a financing gap, the investor will provide funds only if the firm invests at a scale large enough to generate the revenue that enables the firm to repay. We test our theory using a data set with close to 100,000 firm-year observations. The data strongly support our predictions. Among other results, we find a negative relationship between measures of internal funds and investment for a substantial share of financially constrained firms. Our results also help to explain some contrasting findings in the empirical investment literature.Financial constraints, capital market imperfections, financial contracts, investment, internal funds, investment-cash flow sensitivity

Spectral Methods for Correlated Topic Models

In this paper, we propose guaranteed spectral methods for learning a broad range of topic models, which generalize the popular Latent Dirichlet Allocation (LDA). We overcome the limitation of LDA to incorporate arbitrary topic correlations, by assuming that the hidden topic proportions are drawn from a flexible class of Normalized Infinitely Divisible (NID) distributions. NID distributions are generated through the process of normalizing a family of independent Infinitely Divisible (ID) random variables. The Dirichlet distribution is a special case obtained by normalizing a set of Gamma random variables. We prove that this flexible topic model class can be learned via spectral methods using only moments up to the third order, with (low order) polynomial sample and computational complexity. The proof is based on a key new technique derived here that allows us to diagonalize the moments of the NID distribution through an efficient procedure that requires evaluating only univariate integrals, despite the fact that we are handling high dimensional multivariate moments. In order to assess the performance of our proposed Latent NID topic model, we use two real datasets of articles collected from New York Times and Pubmed. Our experiments yield improved perplexity on both datasets compared with the baseline

Efficient cost sharing with a cheap residual claimant

For the cooperative production problem where the commons is a one dimensional convex cost function, I propose the residual mechanism to implement the efficient production level . In contrast to the familiar cost sharing methods such as serial, average and incremental, the residual mechanism may subsidize an agent with a null demand. IFor a large class of smooth cost functions, the residual mechanism generates a budget surplus that is, even in the worst case, vanishes as 1/logn where n is the number of participants. Compare with the serial, average and incremental mechanisms, of which the budget surplus, in the worst case, converges to the efficient surplus as n grows. The second problem is the assignment among n agents of p identical objects and cash transfers to compensate the losers. We assume pn/2, it may even fail to achieve voluntary participation

A Model of Quantum Economic Development

Quantum Economic Development (or the QED MODEL) is an entirely new field of theoretical economic conceptualisation into the evolutionary end point of the New Global Economy. A full description of the process of forming a kernel of fundamental 'quantum like' logic of the architecture and mechanics of these totally new quantum economies is included, as well as some of the more urgent and suggested effects on Humanity. The interdisciplinary boundaries of Free Market Economics and Quantum Physics have been dissolved through conceptual multi-dimensional and multi-scalar relationships and by constructing a model to explain how these systems could work for a global society of up to one hundred billion market participants. Light speed and internet based virtual economies (mostly corporate in nature) are on our combined global event horizon. This paper is prepared for global Academic, Business, Community and Development leaders to understand the basics of Quantum State Economies and their eventual march toward 'Economic Fusion' sometime in this first half of this century. These virtual economic environments spanning the global may allow us for the first time to meet the basic criteria of a free market economy and simultaneously the pre-engineering of the light speed evolution of ideas to their commercial manifestation. As we now learn from present economic malfunctions, phenomena that were once regarded as only concepts, are being created by the en masse interactions of market forces and energies that may begin to act according to ‘quantum like’ relationships. A vital paper for decision makers of all walks of life.qed, theorem, model, quantum, economic, development, new, gobal, economy, economies, light, speed, e-commerce, internet, mass, markets, interactive, trading, einstein, smith, wealth, nations, government, intervention,universal, currency, units, business, templates, forces, energies, fusion, fission, force, belonging, developing

TumbleBit: an untrusted Bitcoin-compatible anonymous payment hub

This paper presents TumbleBit, a new unidirectional unlinkable payment hub that is fully compatible with today s Bitcoin protocol. TumbleBit allows parties to make fast, anonymous, off-blockchain payments through an untrusted intermediary called the Tumbler. TumbleBits anonymity properties are similar to classic Chaumian eCash: no one, not even the Tumbler, can link a payment from its payer to its payee. Every payment made via TumbleBit is backed by bitcoins, and comes with a guarantee that Tumbler can neither violate anonymity, nor steal bitcoins, nor print money by issuing payments to itself. We prove the security of TumbleBit using the real/ideal world paradigm and the random oracle model. Security follows from the standard RSA assumption and ECDSA unforgeability. We implement TumbleBit, mix payments from 800 users and show that TumbleBits offblockchain payments can complete in seconds.https://eprint.iacr.org/2016/575.pdfPublished versio

Designing for adaptability in architecture

The research is framed on the premise that designing buildings that can adapt by accommodating change easier and more cost-effectively provides an effective means to a desired end a more sustainable built environment. In this context, adaptability can be viewed as a means to decrease the amount of new construction (reduce), (re)activate underused or vacant building stock (reuse) and enhance disassembly/ deconstruction of components (reuse, recycle) - prolonging the useful life of buildings (reduce, reuse, recycle). The aim of the research is to gain a holistic overview of the concept of adaptability in the construction industry and provide an improved framework to design for, deploy and implement adaptability. An over-arching research question was posited to guide the inquiry: how can architects understand, communicate, design for and test the concept of adaptability in the context of the design process? The research followed Dubois and Gadde s (2002) systematic combining as an over-arching approach that continuously moves between the empirical world and theoretical models allowing the co-evolution of data collection and theory from the beginning as part of a non-linear process with the objective of matching theory with reality. An initial framework was abducted from a preliminary collection of data from which a set of mixed research methods was deployed to explore adaptability (interviews, building case studies, dependency structural matrices, practitioner surveys and workshop). Emergent from the data is an expanded and revised theory on designing for adaptability consisting of concepts, models and propositions. The models illustrate many of the casual links between the physical design structure of the building (e.g. plan depth, storey height) and the soft contingencies of a messy design/construction/occupation process (e.g. procurement route, funding methods, stakeholder mindsets). In an effort to enhance building adaptability, the abducted propositions suggest a shift in the way the industry values buildings and conducts aspects of the design process and how designer s approach designing for adaptability