arXiv subjects

Asem Hassan

Publications and source records attributed to Asem Hassan.

2 recordsLinked to original sources

arXiv2023

Measuring gravitational force from Femto-gram source masses

Gravity is the weakest of all known forces. Measuring the force of gravity from micro and nano-scale source masses is an essential first step toward low-energy quantum gravity tests. In addition, measuring gravitational forces where the center-of-mass inter-distance is at the sub-mm scale extends the experimentally achievable parameter space for tests of Yukawa-like corrections to Newtonian gravity and tests for higher dimensions proposed to resolve the hierarchy problem of fundamental forces. Here, we propose an experiment using two optically trapped particles in ultrahigh vacuum conditions where the center of mass inter-distance is on the order of $10^2 nm$. In the proposed experiment, the source mass is a rotating Janus nano-particle such that the test mass (sensor) experiences a periodic gravitational potential. Using realistic experimental parameters, a signal-to-noise ratio $\geq 1$ is obtained for a Janus particle with radius $\geq 10^2 nm$ and a mass $\geq \text{10 } fg$. The proposed experiment extends the search of Yukawa corrections to gravity at $\approx 10^{-5}$ times gravity regime at $10^{2}nm $ interaction range, opens the door to low energy tests for quantum gravity, and enables direct experimental tests of extra-dimensional solutions to the hierarchy problem.

gr-qc↗

arXiv2021

Quantifying biomolecular diffusion with a "spherical cow" model

The dynamics of biological polymers, including proteins, RNA, and DNA, occur in very high-dimensional spaces. Many naturally-occurring polymers can navigate a vast phase space and rapidly find their lowest free energy (folded) state. Thus, although the search process is stochastic, it is not completely random. Instead, it is best described in terms of diffusion along a downhill free energy landscape. In this context, there have been many efforts to use simplified representations of the energetics, for which the potential energy is chosen to be a relatively smooth function with a global minima that corresponds to the folded state. That is, instead of including every type of physical interaction, the broad characteristics of the landscape are encoded in approximate energy functions. We describe a particular class of models, called structure-based models, that can be used to explore the diffusive properties of biomolecular folding and conformational rearrangements. These energy functions may be regarded as the "spherical cow" for modeling molecular biophysics. We discuss the physical principles underlying these models and provide an entry-level tutorial, which may be adapted for use in curricula for physics and non-physics majors.

physics.comp-ph↗