Logistic Knowledge Tracing: A Constrained Framework for Learner Modeling

Adaptive learning technology solutions often use a learner model to trace learning and make pedagogical decisions. The present research introduces a formalized methodology for specifying learner models, Logistic Knowledge Tracing (LKT), that consolidates many extant learner modeling methods. The strength of LKT is the specification of a symbolic notation system for alternative logistic regression models that is powerful enough to specify many extant models in the literature and many new models. To demonstrate the generality of LKT, we fit 12 models, some variants of well-known models and some newly devised, to 6 learning technology datasets. The results indicated that no single learner model was best in all cases, further justifying a broad approach that considers multiple learner model features and the learning context. The models presented here avoid student-level fixed parameters to increase generalizability. We also introduce features to stand in for these intercepts. We argue that to be maximally applicable, a learner model needs to adapt to student differences, rather than needing to be pre-parameterized with the level of each student's ability

Carbon-cycle feedbacks operating in the climate system

Climate change involves a direct response of the climate system to forcing which is amplified or damped by feedbacks operating in the climate system. Carbon-cycle feedbacks alter the land and ocean carbon inventories and so act to reduce or enhance the increase in atmospheric CO2 from carbon emissions. The prevailing framework for carbon-cycle feedbacks connect changes in land and ocean carbon inventories with a linear sum of dependencies on atmospheric CO2 and surface temperature. Carbon-cycle responses and feedbacks provide competing contributions: the dominant effect is that increasing atmospheric CO2 acts to enhance the land and ocean carbon stores, so providing a negative response and feedback to the original increase in atmospheric CO2, while rising surface temperature acts to reduce the land and ocean carbon stores, so providing a weaker positive feedback for atmospheric CO2. The carbon response and feedback of the land and ocean system may be expressed in terms of a combined carbon response and feedback parameter, λcarbon in units of W m− 2K− 1, and is linearly related to the physical climate feedback parameter, λclimate, revealing how carbon and climate responses and feedbacks are inter-connected. The magnitude and uncertainties in the carbon-cycle response and feedback parameter are comparable with the magnitude and uncertainties in the climate feedback parameter from clouds. Further mechanistic insight needs to be gained into how the carbon-cycle feedbacks are controlled for the land and ocean, particularly to separate often competing effects from changes in atmospheric CO2 and climate forcing

A Contracting, Turbulent, Starless Core in the Serpens Cluster

We present combined single-dish and interferometric CS(2--1) and N2H+(1--0) observations of a compact core in the NW region of the Serpens molecular cloud. The core is starless according to observations from optical to millimeter wavelengths and its lines have turbulent widths and ``infall asymmetry''. Line profile modeling indicates supersonic inward motions v_in>0.34 km/s over an extended region L>12000AU. The high infall speed and large extent exceeds the predictions of most thermal ambipolar diffusion models and points to a more dynamical process for core formation. A short (dynamic) timescale, ~1e5 yr=L/v_in, is also suggested by the low N2H+ abundance ~1e-10.Comment: 11 pages including 2 figures. Accepted for publication in the Astrophysical Journal Letter

A High Resolution Study of the Slowly Contracting, Starless Core L1544

We present interferometric observations of N2H+(1--0) in the starless, dense core L1544 in Taurus. Red-shifted self-absorption, indicative of inward motions, is found toward the center of an elongated core. The data are fit by a non-spherical model consisting of two isothermal, rotating, centrally condensed layers. Through a hybrid global-individual fit to the spectra, we map the variation of infall speed at scales ~1400AU and find values ~0.08 km/s around the core center. The inward motions are small in comparison to thermal, rotational, and gravitational speeds but are large enough to suggest that L1544 is very close to forming a star.Comment: 11 pages, 2 figures Accepted for publication in Astrophysical Journal Letter

Climate sensitivity from both physical and carbon cycle feedbacks

The surface warming response to anthropogenic forcing is highly sensitive to the strength of feedbacks in both the physical climate and carbon cycle systems. However, the definitions of climate feedback, λClimate in W·m−2·K−1, and climate sensitivity, SClimate in K/(W/m2), explicitly exclude the impact of carbon cycle feedbacks. Here we provide a new framework to incorporate carbon feedback into the definitions of climate feedback and sensitivity. Applying our framework to the Global Carbon Budget reconstructions reveals a present‐day terrestrial carbon feedback of λCarbon = 0.31 ± 0.09 W·m−2·K−1 and an ocean carbon feedback of −0.06 to 0.015 W·m−2·K−1 in Earth system models. Observational constraints reveal a combined climate and carbon feedback of λClimate+Carbon = 1.48 W·m−2·K−1 with a 95% range of 0.76 to 2.32 W·m−2·K−1 on centennial time scales, corresponding to a combined climate and carbon sensitivity of SClimate+Carbon = 0.67 K/(W/m2) with a 95% range of 0.43 to 1.32 K/(W/m2)

Continuous-variable quantum key distribution field-test with true local oscillator

Continuous-variable quantum key distribution (CV-QKD) using a true local (located at the receiver) oscillator (LO) has been proposed to remove any possibility of side-channel attacks associated with transmission of the LO as well as reduce the cross-pulse contamination. Here we report an implementation of true LO CV-QKD using "off-the-shelf" components and conduct QKD experiments using the fiber optical network at Oak Ridge National Laboratory. A phase reference and quantum signal are time multiplexed and then wavelength division multiplexed with the classical communications which "coexist" with each other on a single optical network fiber. This is the first demonstration of CV-QKD with a receiver-based true LO over a deployed fiber network, a crucial step for its application in real-world situations

Hepatic effects of tartrazine (E 102) after systemic exposure are independent of oestrogen receptor interactions in the mouse

Tartrazine is a food colour that activates the transcriptional function of the human oestrogen receptor alpha in an in vitro cell model. Since oestrogens are cholestatic, we hypothesised tartrazine will cause periportal injury to the liver in vivo. To test this hypothesis, tartrazine was initially administered systemically to mice resulting in a periportal recruitment of inflammatory cells, increased serum alkaline phosphatase activity and mild periportal fibrosis. To determine whether an oestrogenic effect may be a key event in this response, tartrazine, sulphonated metabolites and a food additive contaminant were screened for their ability to interact with murine oestrogen receptors. In all cases, there were no interactions as agonists or antagonists and further, no oestrogenicity was observed with tartrazine in an in vivo uterine growth assay. To examine the relevance of the hepatic effects of tartrazine to its use as a food additive, tartrazine was orally administered to transgenic NF-κB-Luc mice. Pre- and concurrent oral treatment with alcohol was incorporated given its potential to promote gut permeability and hepatic inflammation. Tartrazine alone induced NF- κB activities in the colon and liver but there was no periportal recruitment of inflammatory cells or fibrosis. Tartrazine, its sulphonated metabolites and the contaminant inhibited sulphotransferase activities in murine hepatic S9 extracts. Given the role of sulfotransferases in bile acid excretion, the initiating event giving rise to periportal inflammation and subsequent hepatic pathology through systemic tartrazine exposure is therefore potentially associated an inhibition of bile acid sulphation and excretion and not on oestrogen receptor-mediated transcriptional function. However, these effects were restricted to systemic exposures to tartrazine and did not occur to any significant effect after oral exposure