Carsten Krabbe Nielsen

Molecular Photoacoustic Imaging of Follicular Thyroid Carcinoma

Purpose: To evaluate the potential of targeted photoacoustic imaging as a noninvasive method for detection of follicular thyroid carcinoma. Experimental Design: We determined the presence and activity of two members of matrix metalloproteinase family (MMP), MMP-2 and MMP-9, suggested as biomarkers for malignant thyroid lesions, in FTC133 thyroid tumors subcutaneously implanted in nude mice. The imaging agent used to visualize tumors was MMP-activatable photoacoustic probe, Alexa750-CXeeeeXPLGLAGrrrrrXK-BHQ3. Cleavage of the MMP-activatable agent was imaged after intratumoral and intravenous injections in living mice optically, observing the increase in Alexa750 fluorescence, and photoacoustically, using a dual-wavelength imaging method. Results: Active forms of both MMP-2 and MMP-9 enzymes were found in FTC133 tumor homogenates, with MMP-9 detected in greater amounts. The molecular imaging agent was determined to be activated by both enzymes in vitro, with MMP-9 being more efficient in this regard. Both optical and photoacoustic imaging showed significantly higher signal in tumors of mice injected with the active agent than in tumors injected with the control, nonactivatable, agent. Conclusions: With the combination of high spatial resolution and signal specificity, targeted photoacoustic imaging holds great promise as a noninvasive method for early diagnosis of follicular thyroid carcinomas. Clin Cancer Res; 19(6); 1494–502. ©2013 AACR.

On rationally confident beliefs and rational overconfidence

The starting point for rational beliefs models is the existence of an empirical distribution for the stochastic process of observed exogenous and endogenous variables. Since the true, unknown stochastic process that generates this observed empirical distribution is only weakly asymptotic mean stationary (WAMS), i.e. not necessarily stationary, there are many possible processes that could have lead to this empirical distribution. The distribution of any process that is, in this sense, compatible with observations is called a rational belief. We provide a characterization of WAMS processes that among other things leads us to link rational beliefs and overconfidence: Rational beliefs exhibit rational confidence and, since different agents may hold different rational beliefs, the resulting diversity gives rise to rational overconfidence at the social level. In sum, the stylized facts of diversity of beliefs and overconfidence are replicated by rational belief models.

On some topological properties of stable measures

SummaryThe paper shows that the set of stable probability measures and the set of Rational Beliefs relative to a given stationary measure are closed in the strong topology, but not closed in the topology of weak convergence. However, subsets of the set of stable probability measures which are characterized by uniformity of convergence of the empirical distribution are closed in the topology of weak convergence. It is demonstrated that such subsets exist. In particular, there is an increasing sequence of sets of SIDS measures whos union is the set of all SIDS measures generated by a particular system and such that each subset consists of stable measures. The uniformity requirement has a natural interpretation in terms of plausibility of Rational Beliefs.

Sunspot Rational Beliefs Structures, Equilibria and Excess Volatility

In rational beliefs (RB) models there is an observed empirical distribution for the stochastic process of state variables. Many different weakly asymptotic mean stationary (WAMS) processes could have generated this empirical distribution, i.e. are consistent with it, and each of them are therefore called a rational belief.We provide a general framework for using RB in general equilibrium models. Individual rational beliefs are assumed correlated by means of sunspots which at the aggregate level lead to excess volatility.The application adapts the proof by Duffie et al (1994) of the existence of a stationary ergodic RE equilibrium to the case where agents hold rational beliefs.

Bank Regulation When Both Deposit Rate Control and Capital Requirements are Socially Costly

We provide a welfare comparison of the two types of banking regulation commonly used to address moral hazard problems, deposit rate ceilings and minimum capital requirements. It is well understood that interference with the price mechanism may lead to inefficiencies -- in the case of a deposit rate ceiling, the expected consequence is financial repression and possibly migration of depositors to unregulated financial institutions. As was already pointed out by Besanko and Thakor (1992), minimum capital requirements are, however, likely to have similar effects, since banks will pass the costs of this regulation on to depositors in the form of lower interest rates. Possibly for this reason there seem to be no theoretical studies supporting the reforms in the 80s and 90s, which saw deposit rate ceilings being replaced by minimum capital requirements. Either the two instruments are considered for all practical purposes equivalent or the conclusion is in favor of deposit regulation. In our model, while both types of regulation may depress deposit rates, there is a real trade-off between the two: capital regulation is costly because the opportunity costs of capital is higher than the return from normal banking activities while deposit rate ceilings may result in an inefficiently high number of banks. We show that, depending on the opportunity costs of banking capital and on the severity of the moral hazard problem they seek to address, each of the two regulatory instruments may welfare dominate the other.

Bank Regulation in a Complex Environment

We study risk based capital requirements in a monopolistic competition, general equilibrium model. Banks may invest in suboptimal gambling assets rather than risky assets (which we interpret as lending to firms). Capital requirements are used to address this moral hazard problem but may (inadvertently) induce banks to switch into a class of safe assets which are not subject to capital requirements but not optimal either.Our model may contribute to the understanding of the recent contraction in bank funds to European firms despite the quantitative easing by the European Central Bank. Our model suggests as explanation the very design of the Basel accords rather than procyclicality in the traditional sense.Furthermore, since optimizing banks may choose to voluntarily hold capital buffers in response to increased capital requirements, our model also provides a perspective on the new mandatory capital buffers under Basel III.

The Loan Contract with Costly State Verification and Subjective Beliefs

We provide a characterization of the optimal loan contract with costly state verification for the bank when the entrepreneur is risk averse and holds a belief different from that of the bank.

Optimal Exchange Rate Regimes: Sunspots, Currency Crises, and Welfare

In this two country OLG model there is a potential role for active governments since markets are incomplete. There are many coordinated policies (exchange rate regimes) that result in an optimal allocation if extrinsic uncertainty plays no role. However, if we take into account the possibility of sunspot equilibria, the set of optimal policies is drastically reduced. Whenever there is a possibility of influence by extrinsic uncertainty, one or both governments may seek to avoid this by intervening on the foreign exchange markets. When only one country does so, this may lead to a currency crisis, where the central bank is active and is with positive probability unsuccessful in its attempt to defend its currency. If the two countries form a monetary union, a coordinated fiscal policy is needed as a substitute for an optimal exchange rate regime.