arXiv subjects

Yoav Green

Publications and source records attributed to Yoav Green.

At least 19 recordsLinked to original sources

arXiv2026

The transmembrane potential across a charged nanochannel subjected to asymmetric electrolytes

The transmembrane voltage, $V$, which is the potential drop required to nullify the electrical current ($i=0$), is a key characteristic of water desalination and energy harvesting systems that utilize macroscopically large nanoporous membranes, as well as for physiological ion channels subjected to asymmetric salt concentrations. To date, existing analytical expressions for $V_{i=0}$ have been limited to simple scenarios or under simplifying assumptions. In this work, we derive two expressions for $V_{i=0}$. First, we consider the much simpler scenario of two species. Then, we can consider an electrolyte comprised of an arbitrary number of species. The difference in the models is that the latter solution utilizes an ad-hoc assumption of a linear concentration profile, while the former solution does not require such an ad-hoc assumption. We analyze both models and show how to reduce them to several known models. We also verify both models with numerical simulations of the one-dimensional Poisson-Nernst-Planck equations. We show how the interplay between diffusion coefficients and ionic valencies significantly varies the system response and why it is essential to account for all system parameters. Ultimately, this model can be used to improve experimental interpretation of ion transport measurements

cond-mat.mes-hall↗

arXiv2025

Is the Goldman-Hodgkin-Katz equation universally true?

No. Eighty years ago, the two seminal works by Goldman [J. Gen. Phys. 27, 37 (1943)] and by Hodgkin-Katz [J. of Physio 108, 37 (1949)] derived the foundational framework for interpreting electro-physiological measurements in what is commonly termed the Goldman-Hodgkin-Katz (GHK) theory for the membrane potential. Both seminal papers postulate a constant/uniform electric field within the ion channel. Using a uniform electric field allows for a simple, straightforward calculation of the ionic fluxes and the transmembrane potential, which yields the famous GHK potential. The use of this framework is so widely accepted that one can find a plethora of works that no longer cite the original works and GHK has perhaps become the universal and indisputable descriptor of the underlying physics and biology. In recent works [Phys. Rev. Lett. 134, 228401 (2025) and Phys. Rev. E 111, 064408 (2025)], we revisited GHK and its assumption of a uniform field. Non-approximated numerical simulations showed that the electric field is not always uniform. To understand this discrepancy, it is important to understand that the governing equations can be solved using two different approaches: the GHK approach of assuming a constant electric field or postulating that the system is electroneutral. Each approach yields drastically different non-commutative results. The purpose of this report is to provide a non-mathematical summary of the results and to inform the broader community that GHK is not as universal as previously thought. We will discuss these two newer works, with some emphasis on how they can potentially revolutionize the interpretation of electro-physiological measurements. Importantly, we show that this new framework, which utilizes the mathematical tools developed by the electrodialysis community, also serves as a bridge linking the electrophysiology community and the electrodialysis community.

physics.bio-ph↗

arXiv2025

Towards a unified mechanistic understanding of the electrical response of bipolar nanofluidic systems

Bipolar nanoporous membranes and bipolar nanochannels are used in water desalination and energy-harvesting systems that provide clean water and green energy, respectively. The growing need for both requires continuous improvement of their performance. However, the underlying physics of these complex systems is still not fully understood, making empirical optimization slow and inefficient. In this work, we combine theoretical analysis and numerical simulations to develop a unified framework for improving the design of nanofluidic devices. We show that the system response is governed by the interplay between the applied voltage and a parameter $\eta$, which depends on the ratio of geometry and surface charge densities of both charged regions. At low voltages, the response is mostly determined by $\eta$, allowing its dependence to be represented by a simplified phase space. At high voltages, this phase space becomes oversimplified. To demonstrate the framework's robustness, we scan a range of configurations, from unipolar channels (single charged region) to bipolar channels (positive and negative segments). We compare the numerically simulated current-voltage responses with three theoretical models, which are limiting scenarios within the phase space, and explain the observed deviations. These findings can help reduce the time and resources required to optimize nanofluidic devices and improve the interpretation of experiments and simulations.

cond-mat.mes-hall↗

arXiv2024

The Goldman-Hodgkins-Katz Equation, Reverse-Electrodialysis, and Everything in Between

In the past eighty years, the Goldman-Hodgkins-Katz (GHK) equation has been the gold-standard framework for interpreting countless biological and physiological experiments and simulations that involve ion transport in nanopores/nanochannels/ion-channels subjected to a combined ionic concentration and electric potential gradients. In this work, we revisit the mathematical derivation used to develop the GHK model and show that this model is internally inconsistent. In particular, we show that its infamous assumption of a constant electric field is incorrect, which leads to substantial errors, including the inability of this model to satisfy local and global electroneutrality. Then, leveraging key insights from the field of reverse electrodialysis (RED), we derive a new internally consistent model that does not assume that the electric field is constant and satisfies electroneutrality. This new model has several advantages. First, while the mathematics are substantially more complicated, the derivation does not include ad-hoc assumptions, and the model is internally consistent. Second, the new solution connects the two realms of GHK and RED, which consider the same equations but in opposing limits, negligible or substantial surface charge density effects, respectively. Third, while the expressions for the new model are complicated, the new model can be reduced to several limits, which allows for a much easier and more straightforward analysis. Finally, all of our newly derived results show remarkable correspondence to non-approximated numerical simulations. This work provides a brand-new framework for interpreting (and reinterpreting) ion transport experiments in any charge-selective system.

physics.bio-ph↗

arXiv2024

Electrical Response of Nanofluidic Systems Subjected to Viscosity Gradients

It is expected that the introduction of a viscosity gradient across a nanofluidic system will drastically vary its current-voltage response, $i-V$. However, to date, there is no self-consistent theoretical model that can be used to fully characterize such a system. This work provides an internally self-consistent model that details all the key characteristics of ion transport through a nanofluidic system for an arbitrary viscosity field. In particular, this work addresses three separate issues. First, we provide a new expression for the Ohmic conductance, $g_{Ohmic} = i/V$. Second, several previous theoretical studies have suggested that the introduction of a viscosity gradient can result in the shift of the $i-V$ such that it does not cross the origin. This work unequivocally shows that the $i-V$ is expected to always cross the origin. Third, we demonstrate that even without electroosmotic flows, the introduction of a viscosity gradient results in current rectification. Importantly, all theoretical results are verified by non-approximated numerical simulations. This work provides the appropriate framework to analyze and interpret experimental and numerical simulations of nanofluidic systems subject to a viscosity gradient.

cond-mat.mes-hall↗

arXiv2024

Bipolar nanochannels: The effects of an electro-osmotic instability. Part I: Steady-state response

The steady-state current-voltage response of ion-selective systems varies as the number of ion-selective components is varied. For the highly investigated unipolar system, including only one ion-selective component, it has been shown that above a supercritical voltage, an electroosmotic instability is triggered, leading to over-limiting currents. In contrast, the effects of this instability on the current-voltage response of the second most common system of a bipolar system, including two oppositely charged permselective regions, have yet to be reported. Using simulations, we investigate the steady-state electrical response of bipolar systems as we vary the ratio of the charge within the two oppositely charged regions. The responses are divided into those with an internal symmetry related to the surface charge and those without. In contrast to the unipolar systems, bipolar systems with the internal symmetry do not exhibit overlimiting currents, and their steady-state response is identical to the convectionless steady-state response. In contrast, the systems without the internal symmetry exhibit much more complicated behavior. For positive voltages, they have overlimiting currents, while for negative voltages, they do not have over-limiting currents. Our findings contribute to a more profound understanding of the behavior of the current-voltage response in bipolar systems.

cond-mat.mes-hall↗

arXiv2024

Bipolar nanochannels: The effects of an electro-osmotic instability. Part II: Time-transient response

The most common method to characterize the electrical response of a nanofluidic system is through its steady-state current-voltage response. In Part I, we demonstrated that this current-voltage response depends on the geometry, the layout of the surface charge, and the effects of advection. We demonstrated that each configuration has a unique steady-state signature. Here, we will elucidate the behavior of the time-transient response. Similar to the steady-state response, we will show that each configuration has its own unique time-transient signature when subjected to electroosmotic instability. We show that bipolar systems behave differently than unipolar systems. In unipolar systems, the instability appears only at one end of the system. In contrast, in bipolar systems the instability will either appear on both sides of the nanochannel or not at all. If it does appear on both sides, the instability will eventually vanish on one or both sides of the system. In Part I, these phenomena were explained using steady-state considerations of the behavior of the fluxes. Here, we will examine the time-transient behavior to reveal the governing principles that are, on the one hand, not so different from unipolar systems and, on the other hand, remarkably different.

cond-mat.mes-hall↗

arXiv2024

Electrical Conductance of Nanofluidic Systems subjected to Asymmetric Concentrations

A nanochannel subjected to both a potential and concentration gradient has an asymmetric current-voltage, I-V, response with three primary characteristics: the Ohmic conductance, G, the current at zero voltage, I(v=0), and the voltage at zero current, V(I=0). To date, there is no known self-consistent theory for these characteristics subject to an arbitrary concentration gradient. Here, we present simple expressions for each of these characteristics that have been derived self-consistently. Our findings provide insights into the underlying physics of nanofluidics systems used for water desalination and energy harvesting.

cond-mat.mes-hall↗

arXiv2022

Electrical Circuit Modelling of Nanofluidic Systems

Nanofluidic systems exhibit transport characteristics that have made technological marvels such as desalination, energy harvesting, and highly sensitive biomolecule sensing possible by virtue of their ability to influence small currents due to the selective transport of ions. Traditionally many of these applications have relied on the use of nanoporous membranes. The immense complexities of membrane geometry often impede a comprehensive understanding of the underlying physics. To bypass the associated difficulties, here we consider the much simpler nanochannel array comprised of numerous nanochannels and elucidate the effects of interchannel interactions on the Ohmic response of the array. We demonstrate that a nanochannel array is equivalent to an array of mutually independent but identical unit-cells whereby the array can be represented by an equivalent electrical circuit of unit-cell resistances connected in a parallel configuration. We show that the total resistance of the system scales inversely to the number of channels. We further deconstruct the unit-cell to be a combination of multiple contributing resistances connected in series. We validate the theoretical model underlying these electrical abstractions using numerical simulations and experiments. Our approach to modeling realistic nanofluidic systems by their equivalent electrical circuit provides an invaluable tool for analyzing and interpreting experimental measurements, characterization of surface charge properties of newly developed materials, and a method for the design and development of function-specific nanofluidic devices.

physics.flu-dyn↗

arXiv2022

Electrical conductance of charged nanopores

A nanopores's response to an electrical potential drop is characterized by its electrical conductance, \tilde{G}. It has long been thought that at low concentrations, the conductance is independent of the electrolyte concentration, \tilde{c}_0, such that \tilde{G} ~ \tilde{c}_0^0. It has been recently demonstrated that surface charge regulation changes the dependency to be \tilde{G} ~ \tilde{c}_0^{\alpha} where the slope typically takes the values \alpha = 1/3 or 1/2. Yet, experiments have observed slopes of 2/3 and 1 suggesting that additional mechanisms, such as convection and slip-lengths, appear. We show that the inclusion of convection doesn't vary the slope, while the inclusion of a slip length doubles the slope value. Here, we elucidate the interplay between surface charge regulation, convection, and slip-lengths. We show that when all effects are accounted for \alpha can take any value between 0 and 1. This result is of utmost importance in designing any electro-kinetically driven nanofluidic system characterized by its conductance.

physics.flu-dyn↗

arXiv2020

The Palomar Transient Factory Core-Collapse Supernova Host-Galaxy Sample. I. Host-Galaxy Distribution Functions and Environment-Dependence of CCSNe

Several thousand core-collapse supernovae (CCSNe) of different flavors have been discovered so far. However, identifying their progenitors has remained an outstanding open question in astrophysics. Studies of SN host galaxies have proven to be powerful in providing constraints on the progenitor populations. In this paper, we present all CCSNe detected between 2009 and 2017 by the Palomar Transient Factory. This sample includes 888 SNe of 12 distinct classes out to redshift $z\approx1$. We present the photometric properties of their host galaxies from the far-ultraviolet to the mid-infrared and model the host-galaxy spectral energy distributions to derive physical properties. The galaxy mass functions of Type Ic, Ib, IIb, II, and IIn SNe ranges from $10^{5}$ to $10^{11.5}~M_\odot$, probing the entire mass range of star-forming galaxies down to the least-massive star-forming galaxies known. Moreover, the galaxy mass distributions are consistent with models of star-formation-weighted mass functions. Regular CCSNe are hence direct tracers of star formation. Small but notable differences exist between some of the SN classes. Type Ib/c SNe prefer galaxies with slightly higher masses (i.e., higher metallicities) and star-formation rates than Type IIb and II SNe. These differences are less pronounced than previously thought. H-poor SLSNe and SNe~Ic-BL are scarce in galaxies above $10^{10}~M_\odot$. Their progenitors require environments with metallicities of $<0.4$ and $<1$ solar, respectively. In addition, the hosts of H-poor SLSNe are dominated by a younger stellar population than all other classes of CCSNe. Our findings corroborate the notion that low-metallicity \textit{and} young age play an important role in the formation of SLSN progenitors.

astro-ph.GA↗

arXiv2020

On the relationship between velocities, tractions, and intercellular stresses in the migrating epithelial monolayer

The relationship between velocities, tractions, and intercellular stresses in the migrating epithelial monolayer are currently unknown. Ten years ago, a method known as Monolayer Stress Microscopy (MSM) was suggested from which the intercellular stresses could be computed given a traction field. The core assumption of MSM is that the intercellular stresses within the monolayer behave similarly to passive systems like a Hookean solid (an elastic sheet) or a Newtonian fluid (thin fluid film), implying a relation between the displacements/velocities and tractions. Due to the lack of independently measured intercellular stresses, validation of MSM is difficult. An alternative approach, which we give here, is based on simultaneous measurements of the monolayer velocity field and the cell/substrate tractions. With limited assumptions, the velocity field suffices to compute tractions, which we can then compare directly with those measured by traction force microscopy. We find that the calculated tractions and measured tractions are uncorrelated. Since both classical MSM and a purely viscous description of the relation between displacements or velocities and tractions depends on a linear constitutive law, it follows that some modification of these approaches is needed. One possible resolution is the inclusion of an active force. To this end, we give a new relationship between the active force density and the measured velocity(or displacement) field, and tractions, which by Newton's laws, must be obeyed.

physics.bio-ph↗

arXiv2019

Revisiting, resolving and unifying the nanochannel-microchannel electrical resistance paradigm

Until recently, the accepted paradigm was that the Ohmic electrical response of nanochannel-microchannel systems is determined solely by the nanochannel while the effects of the adjacent microchannels are negligible. Two, almost identical, models were suggested to rationalize experimental observations that appeared to confirm the paradigm. However, recent works have challenged this paradigm and shown that the microchannels contribute in a non-negligible manner, and thus these two models are inadequate in describing realistic nanochannel-microchannel systems. Two newer nanochannel-microchannel models were suggested to replace the nanochannel-dominant models. These models were limited to either very low or very high concentrations. Here, we review these four leading models. The most popular is shown to be incorrect, while the remaining models are unified under a newly derived solution which shows remarkable correspondence to simulations and experiments. The unifying model can be used to improve the design of any nanofluidic based systems as the physics are more transparent, and the need for complicated time-consuming preliminary simulations and experiments has been eliminated.

physics.app-ph↗

arXiv2015

Time-dependent ion transport in heterogeneous permselective systems

The current study extends previous analytical and numerical solutions of chronopotentiometric response of one-dimensional systems consisting of three layers to the more realistic two-dimensional heterogeneous ion-permselective medium. An analytical solution for the transient concentration-polarization problem, under the local electro-neutrality approximation and ideal permselectivity, was obtained using the Laplace transform and separation of variables. Then the two-dimensional electric potential was obtained numerically and was compared to the full Poisson-Nernst-Planck solution. It was then shown that the resultant voltage drop across the system varies between the initial Ohmic response and that of the steady-state accounting for concentration-polarization. Also, field-focusing effect in a two-dimensional system is shown to result in a faster depletion of ions at the permselective interface.

physics.flu-dyn↗

arXiv2014

Bridging the Gap between an Isolated Nanochannel/pore System and Communicating Multipore Heterogeneous Membrane System

To bridge the gap between single/isolated pore systems to multi-pore systems, such as membranes/electrodes, we studied an array of nanochannels with varying interchannel spacing that controlled the degree of channel communication. Instead of treating them as individual channels connected in parallel or an assembly like a homogeneous membrane, this study resolves the pore-pore interaction. We found that increased channel isolation leads to current intensification whereas at high voltages electro-convective effects control the degree of communication via suppression of the diffusion layer growth

physics.flu-dyn↗

arXiv2014

Effect of geometry on concentration polarization in realistic heterogeneous permselective systems

This study extends previous analytical solutions of concentration-polarization occurring solely in the depleted region, to the more realistic geometry consisting of a three dimensional (3D) heterogeneous ion-permselective medium connecting two opposite microchambers (i.e. 3 layers system). Under the local electro-neutrality approximation, the separation of variable methods is used to derive an analytical solution of the electro-diffusive problem for the two opposing asymmetric microchambers. Assuming an ideal permselective medium allows for the analytic calculation of the 3D concentration and electric potential distributions as well as a current-voltage relation. It is shown that any asymmetry in the microchamber geometries will result in current rectification. Moreover, it is demonstrated that for non-negligible microchamber resistances the conductance does not exhibit the expected saturation at low concentrations but instead shows a continuous decrease. The results are intended to facilitate a more direct comparison between theory and experiments as now the voltage drop is across a realistic 3D and 3-layer system.

physics.flu-dyn↗

arXiv2011

PTF10iya: A short-lived, luminous flare from the nuclear region of a star-forming galaxy

We present the discovery and characterisation of PTF10iya, a short-lived (dt ~ 10 d, with an optical decay rate of ~ 0.3 mag per d), luminous (M_g ~ -21 mag) transient source found by the Palomar Transient Factory. The ultraviolet/optical spectral energy distribution is reasonably well fit by a blackbody with T ~ 1-2 x 10^4 K and peak bolometric luminosity L_BB ~ 1-5 x 10^44 erg per s (depending on the details of the extinction correction). A comparable amount of energy is radiated in the X-ray band that appears to result from a distinct physical process. The location of PTF10iya is consistent with the nucleus of a star-forming galaxy (z = 0.22405 +/- 0.00006) to within 350 mas (99.7 per cent confidence radius), or a projected distance of less than 1.2 kpc. At first glance, these properties appear reminiscent of the characteristic "big blue bump" seen in the near-ultraviolet spectra of many active galactic nuclei (AGNs). However, emission-line diagnostics of the host galaxy, along with a historical light curve extending back to 2007, show no evidence for AGN-like activity. We therefore consider whether the tidal disruption of a star by an otherwise quiescent supermassive black hole may account for our observations. Though with limited temporal information, PTF10iya appears broadly consistent with the predictions for the early "super-Eddington" phase of a solar-type star disrupted by a ~ 10^7 M_sun black hole. Regardless of the precise physical origin of the accreting material, the large luminosity and short duration suggest that otherwise quiescent galaxies can transition extremely rapidly to radiate near the Eddington limit; many such outbursts may have been missed by previous surveys lacking sufficient cadence.

astro-ph.HE↗

arXiv2011

Real-Time Detection and Rapid Multiwavelength Follow-up Observations of a Highly Subluminous Type II-P Supernova from the Palomar Transient Factory Survey

The Palomar Transient Factory (PTF) is an optical wide-field variability survey carried out using a camera with a 7.8 square degree field of view mounted on the 48-in Oschin Schmidt telescope at Palomar Observatory. One of the key goals of this survey is to conduct high-cadence monitoring of the sky in order to detect optical transient sources shortly after they occur. Here, we describe the real-time capabilities of the PTF and our related rapid multiwavelength follow-up programs, extending from the radio to the gamma-ray bands. We present as a case study observations of the optical transient PTF10vdl (SN 2010id), revealed to be a very young core-collapse (Type II-P) supernova having a remarkably low luminosity. Our results demonstrate that the PTF now provides for optical transients the real-time discovery and rapid-response follow-up capabilities previously reserved only for high-energy transients like gamma-ray bursts.

astro-ph.CO↗