Crowd Sensors Research Articles

Excluded-volume effects in living cells.

Biomolecules evolve and function in densely crowded and highly heterogeneous cellular environments. Such conditions are often mimicked in the test tube by the addition of artificial macromolecular crowding agents. Still, it is unclear if such cosolutes indeed reflect the physicochemical properties of the cellular environment as the in-cell crowding effect has not yet been quantified. We have developed a macromolecular crowding sensor based on a FRET-labeled polymer to probe the macromolecular crowding effect inside single living cells. Surprisingly, we find that excluded-volume effects, although observed in the presence of artificial crowding agents, do not lead to a compression of the sensor in the cell. The average conformation of the sensor is similar to that in aqueous buffer solution and cell lysate. However, the in-cell crowding effect is distributed heterogeneously and changes significantly upon cell stress. We present a tool to systematically study the in-cell crowding effect as a modulator of biomolecular reactions.

Robust Spectrum Sensing With Crowd Sensors

This paper investigates the issue of cooperative spectrum sensing with a crowd of low-end personal spectrum sensors (such as smartphones, tablets, and in-vehicle sensors), where the sensing data from crowd sensors that may be unreliable, untrustworthy, or even malicious. Moreover, due to either unexpected equipment failures or malicious behaviors, every crowd sensor could sporadically and randomly contribute with abnormal data, which makes the existing cooperative sensing schemes ineffective. To tackle these challenges, we first propose a generalized modeling approach for sensing data with an arbitrary abnormal component. Under this model, we then analyze the impact of general abnormal data on the performance of the cooperative sensing, by deriving closed-form expressions of the probabilities of global false alarm and global detection. To improve sensing data quality and enhance cooperative sensing performance, we further formulate an optimization problem as stable principal component pursuit, and develop a data cleansing-based robust spectrum sensing algorithm to solve it, where the under-utilization of licensed spectrum bands and the sparsity of nonzero abnormal data are jointly exploited to robustly cleanse out the potential nonzero abnormal data component from the original corrupted sensing data. Extensive simulation results demonstrate that the proposed robust sensing scheme performs well under various abnormal data parameter configurations.

The Hollow Domain of the Mechanosensitive Channel MscS is a Sensor of Cytoplasmic Crowding

Mechanosensitive channel MscS is a ubiquitous osmolyte release valve found in walled cells, from bacteria to higher plants. In excised patches, applied tension of 5-8 mN/m activates E. coli MscS, followed by adaptive closure and complete inactivation, both of which are strongly promoted by crowding agents in the cytoplasm and by depolarizing voltages. Previous genetic screens1 and models derived from the crystal structure suggest allosteric coupling between the cytoplasmic ‘cage’ domain and the gate through association of the beta domain and the cytoplasmic end of the pore-lining TM3 helix. This association imposes kinks on TM3 that lead to closing or inactivation. Our analysis shows that mutations disrupting the TM3-beta association dramatically decrease closing rates, impede inactivation and make the channel insensitive to crowding agents and voltage. Conversely, mutations predicted to strengthen the TM3-beta interactions make the channel hard to open and inactivate silently under ramp stimulation. Models with straightened TM3s and separated beta domains representing the resting and open states are supported by an engineered salt bridge, which was not observed in the crystal structure and strongly destabilized the open state. Simulations suggest that in the resting state, with beta domains separated from TM3, the cage is prolate in shape, protruding more into the cytoplasm, whereas conversion to an oblate shape and approaching the membrane favors TM3b-beta association. We conclude that the shape changes make the cage an intracellular crowding sensor which functions through labile kink-stabilizing TM3-beta interactions. The cage is the first example of a hollow channel domain that can provide feedback on the degree of cytoplasm condensation (crowding) that disengages the gate and prevents efflux of osmolytes.1. Koprowski P, Grajkowski W, Isacoff EY and Kubalski A. 2011. J Biol Chem. 286:877-88.

Art applications for crowds

AbstractWe have developed two different art applications as a way of guiding and testing of our technical work in crowd simulation and interface devices. In this paper, we describe both of them as well as the systems used to implement them. ‘Crowds’ is an immersive art installation with stereo projection based on our development of the specification of crowd behavior using XML and images, a proprietary tangible wind interface, and interactive real-time navigation. ‘UnderCrowds’ deals with large crowds, implemented in the graphics processor, and uses a crowd sensor to make the size of the virtual crowd proportional to the number of spectators crossing in front of the said sensor.