The difficulty of folding self-folding origami

Why is it difficult to refold a previously folded sheet of paper? We show that even crease patterns with only one designed folding motion inevitably contain an exponential number of `distractor' folding branches accessible from a bifurcation at the flat state. Consequently, refolding a sheet requires finding the ground state in a glassy energy landscape with an exponential number of other attractors of higher energy, much like in models of protein folding (Levinthal's paradox) and other NP-hard satisfiability (SAT) problems. As in these problems, we find that refolding a sheet requires actuation at multiple carefully chosen creases. We show that seeding successful folding in this way can be understood in terms of sub-patterns that fold when cut out (`folding islands'). Besides providing guidelines for the placement of active hinges in origami applications, our results point to fundamental limits on the programmability of energy landscapes in sheets.Comment: 8 pages, 5 figure

Learned multi-stability in mechanical networks

We contrast the distinct frameworks of materials design and physical learning in creating elastic networks with desired stable states. In design, the desired states are specified in advance and material parameters can be optimized on a computer with this knowledge. In learning, the material physically experiences the desired stable states in sequence, changing the material so as to stabilize each additional state. We show that while designed states are stable in networks of linear Hookean springs, sequential learning requires specific non-linear elasticity. We find that such non-linearity stabilizes states in which strain is zero in some springs and large in others, thus playing the role of Bayesian priors used in sparse statistical regression. Our model shows how specific material properties allow continuous learning of new functions through deployment of the material itself

Brain-Penetrating Histone Deacetylase Inhibitor RG2833: A Potential Malignant Melanoma Growth Suppressor

Histone deacetylases (HDACs) play an important role in the epigenetic control of gene expression in both normal and cancer cells. Previous studies have demonstrated that pharmaceutical inhibition of HDACs can kill and/or suppress the growth of cancer cells. RG2833 is a HDAC inhibitor that targets specific HDACs known to be active in cancer cells. Melanoma cells have previously been shown to respond to HDAC inhibitors that are structurally similar to RG2833. We hypothesized that the inhibition of HDAC activity by RG2833 would result in the reduced growth and/or death of cells from the malignant melanoma cell lines SK-MEL-5 and SK-MEL-28. To test our hypothesis, we exposed SK-MEL-5 and SKMEL-28 cells to increasing concentrations of RG2833. We found that concentrations of RG2833 that effectively inhibited HDAC activity also resulted in reduced melanoma cell growth and viability. These results demonstrate the effectiveness of RG2833 in reducing the growth and viability of malignant melanoma cells in vitro and warrant further investigation of the potential therapeutic use of RG2833 and related compounds in the battle against cancer

Five years in: Assessing the impacts of Chicago’s Large Lots Program

Since 2014, the City of Chicago has sold more than 1,200 city-owned vacant properties to same-block landowners in the South and West sides for $1 each. This "Large Lots Program" is part of a national trend in which cities encourage productive reuse of vacant land by heavily discounting the sale of empty lots in distressed neighborhoods to local buyers. These experimental programs present opportunities for marginalized communities such as wealth-building, crime reduction, and increased control of neighborhood change processes. They also present risks and opportunity costs. Despite these trade-offs, vacant land disposition programs have been understudied and no published literature evaluates whether programs actually achieve their stated goals. Using data from a variety of public and private data sources I evaluate the impact of Chicago’s Large Lots program in three economically distressed neighborhoods. I investigate who is buying Large Lots, how many parcels they are buying, and how far they live from the parcels they are purchasing. Additionally, I perform a block-level difference-in-differences analysis to explore whether the program reduces crime. Finally, I examine the potential wealth generation affects for residents of low-income communities using a parcel-based projection of land value changes.Master of City and Regional Plannin

Controlling Oct4 Expression Levels Using Invitrogen’s GeneSwitch™ System

Oct4 is a protein that is involved in the retention of pluripotency in adipose derived stem cells (ADSCs). Despite this knowledge, Oct4’s exact role in the complex system used in maintaining pluripotency is not known. One approach to explore Oct4’s role would be through the use of cellular assays to control the expression of Oct4. This can possibly be accomplished by introducing a biological switch and the gene of interest into ADSCs. In this project, the GeneSwitch™ System is used to ultimately induce Oct4 expression. Before the GeneSwitch™ System can be used, the Oct4 gene is extracted from murine embryonic stem cell (ES) RNA. This ES RNA is then used as a template to create complimentary DNA (cDNA) that can then be used to create an insert with the Oct4 gene. In addition to the cDNA, recognition sites for endonucleases must be added on to fully create the Oct4 insert. This insert could then be placed into one of the GeneSwitch™ System plasmids that have the same recognition sites and placed into ADSCs along with the plasmid that will act as a biological switch. With this system put into ADSCs, it is expected that Oct4 levels will be successfully controlled. Once controlled, Oct4 expression can be tested and investigations can be completed to determine how Oct4 expression levels influence pluripotency of ADSCs. This may have significant impact on the creation of regenerative medicine

Early Initiation of Oral Antihypertensives Reduces Intensive Care Unit Stay and Hospital Cost for Patients with Hypertensive Intracerebral Hemorrhage.

Background/objectiveIntravenous nicardipine infusion is effective for rapid blood pressure control. However, its use requires hemodynamic monitoring in the intensive care unit (ICU) and is associated with high hospital cost. This study aimed to examine the effect of early versus late initiation of oral antihypertensives on ICU length of stay (LOS) and cost of hospitalization in patients with hypertensive intracerebral hemorrhage (ICH).MethodsThis is a single-center retrospective study of patients with hypertensive ICH treated with nicardipine infusion from January 1, 2013, to December 31, 2017. Patients were dichotomized into study and control groups, based on receiving oral antihypertensives within 24 h versus after 24 h of emergency department arrival. Baseline characteristics, duration of nicardipine infusion, LOS in the ICU and hospital, functional outcome at discharge, and hospital cost were compared between the two groups using univariate and multivariate analysis.ResultsA total of 90 patients in the study group and 76 in the control group were identified. There was no significant difference in demographics, past medical history, and initial SBP between the two groups. After adjusting for confounding factors with multivariate regression models, early initiation of oral antihypertensives was associated with significant reductions in duration of nicardipine infusion (55.5 ± 60.1 vs 121.6 ± 141.3 h, p <0.005), nicardipine cost ($14,207 vs$29,299, p < 0.01), ICU LOS (2 vs 5 days, p < 0.005), and cost of hospitalization ($24,564 vs$47,366, p < 0.01). There was no significant difference in adversary renal events, favorable outcomes, and mortality between the two groups.ConclusionsEarly initiation of oral antihypertensives is safe and may have a significant financial impact on patients with hypertensive ICH

The Spitzer South Pole Telescope Deep Field Survey: Linking galaxies and halos at z=1.5

We present an analysis of the clustering of high-redshift galaxies in the recently completed 94 deg$^2$ Spitzer-SPT Deep Field survey. Applying flux and color cuts to the mid-infrared photometry efficiently selects galaxies at $z\sim1.5$ in the stellar mass range $10^{10}-10^{11}M_\odot$, making this sample the largest used so far to study such a distant population. We measure the angular correlation function in different flux-limited samples at scales $>6^{\prime \prime}$ (corresponding to physical distances $>0.05$ Mpc) and thereby map the one- and two-halo contributions to the clustering. We fit halo occupation distributions and determine how the central galaxy's stellar mass and satellite occupation depend on the halo mass. We measure a prominent peak in the stellar-to-halo mass ratio at a halo mass of $\log(M_{\rm halo} / M_\odot) = 12.44\pm0.08$, 4.5 times higher than the $z=0$ value. This supports the idea of an evolving mass threshold above which star formation is quenched. We estimate the large-scale bias in the range $b_g=2-4$ and the satellite fraction to be $f_\mathrm{sat}\sim0.2$, showing a clear evolution compared to $z=0$. We also find that, above a given stellar mass limit, the fraction of galaxies that are in similar mass pairs is higher at $z=1.5$ than at $z=0$. In addition, we measure that this fraction mildly increases with the stellar mass limit at $z=1.5$, which is the opposite of the behavior seen at low-redshift.Comment: 32 pages, 22 figures. Published in MNRA

Understanding extreme quasar optical variability with CRTS: I. Major AGN flares

There is a large degree of variety in the optical variability of quasars and it is unclear whether this is all attributable to a single (set of) physical mechanism(s). We present the results of a systematic search for major flares in AGN in the Catalina Real-time Transient Survey as part of a broader study into extreme quasar variability. Such flares are defined in a quantitative manner as being atop of the normal, stochastic variability of quasars. We have identified 51 events from over 900,000 known quasars and high probability quasar candidates, typically lasting 900 days and with a median peak amplitude of $\Delta m = 1.25$ mag. Characterizing the flare profile with a Weibull distribution, we find that nine of the sources are well described by a single-point single-lens model. This supports the proposal by Lawrence et al. (2016) that microlensing is a plausible physical mechanism for extreme variability. However, we attribute the majority of our events to explosive stellar-related activity in the accretion disk: superluminous supernovae, tidal disruption events, and mergers of stellar mass black holes.Comment: 25 pages, 18 figures, accepted for publication by MNRA