10 research outputs found
Fair Rank Aggregation
Ranking algorithms find extensive usage in diverse areas such as web search,
employment, college admission, voting, etc. The related rank aggregation
problem deals with combining multiple rankings into a single aggregate ranking.
However, algorithms for both these problems might be biased against some
individuals or groups due to implicit prejudice or marginalization in the
historical data. We study ranking and rank aggregation problems from a fairness
or diversity perspective, where the candidates (to be ranked) may belong to
different groups and each group should have a fair representation in the final
ranking. We allow the designer to set the parameters that define fair
representation. These parameters specify the allowed range of the number of
candidates from a particular group in the top- positions of the ranking.
Given any ranking, we provide a fast and exact algorithm for finding the
closest fair ranking for the Kendall tau metric under block-fairness. We also
provide an exact algorithm for finding the closest fair ranking for the Ulam
metric under strict-fairness, when there are only number of groups. Our
algorithms are simple, fast, and might be extendable to other relevant metrics.
We also give a novel meta-algorithm for the general rank aggregation problem
under the fairness framework. Surprisingly, this meta-algorithm works for any
generalized mean objective (including center and median problems) and any
fairness criteria. As a byproduct, we obtain 3-approximation algorithms for
both center and median problems, under both Kendall tau and Ulam metrics.
Furthermore, using sophisticated techniques we obtain a
-approximation algorithm, for a constant , for
the Ulam metric under strong fairness.Comment: A preliminary version of this paper appeared in NeurIPS 202
Controlling the Fate of Protein Corona by Tuning Surface Properties of Nanoparticles
In
a biological environment, the formation of a protein layer (protein
corona) around nanoparticles immensely hampers its targeting capabilities
and efficiency of specific delivery. Rational design of a nanoparticle
remains one of the biggest challenges due to the lack of in-depth
knowledge of the molecular mechanism of this corona formation on the
different nanoparticle surfaces. Using computer simulation and experimental
study, here, we establish for the first time the role of different
surface properties like charge, chain length, architecture, and surface
density of different surfactant molecules in the formation of the
protein corona. We provide insights into the nanoparticle protein
interaction, especially with respect to the structural orientation
of a particular protein (human serum albumin) around a gold nanoparticle.
We also derived the theoretical optimal conditions to avoid this corona
formation. Such an efficient approach can pave the way to engineer
smarter nanoparticles, which will avoid the protein absorption to
keep their original properties unchanged
Carbon Dots for Single-Molecule Imaging of the Nucleolus
Carbon
dots are newly discovered bright fluorescent biolabeling
probes that nonspecifically bind to multiple cellular structures.
Here we report yellow-orange emissive carbon dots that spontaneously
localize inside the nucleolus of HeLa cells, specifically binding
to the RNA. Single-particle measurements of carbon dots show fluorescence-intensity
fluctuations with superior brightness and photostability. These optical
properties were used for performing blinking-assisted localization
microscopy that shows organization of the nucleolar RNA with improved
resolution. Our study opens up the opportunity for single-molecule
imaging and super-resolution microscopy applications using fluorescent
carbon dots
Time-Resolved Emission Reveals Ensemble of Emissive States as the Origin of Multicolor Fluorescence in Carbon Dots
The
origin of photoluminescence in carbon dots has baffled scientists
since its discovery. We show that the photoluminescence spectra of
carbon dots are inhomogeneously broadened due to the slower relaxation
of the solvent molecules around it. This gives rise to excitation-dependent
fluorescence that violates the KashaâVavilov rule. The time-resolved
experiment shows significant energy redistribution, relaxation among
the emitting states, and spectral migration of fluorescence spectra
in the nanosecond time scale. The excitation-dependent multicolor
emission in time-integrated spectra is typically governed by the relative
population of these emitting states
Lanthanide Metal-Organic Frameworks for Multispectral Radioluminescent Imaging
In this report, we describe the X-ray luminescent properties of two lanthanide-based nanoscale metalâframeworks (nMOFs) and their potential as novel platforms for optical molecular imaging techniques such as X-ray excited radioluminescence (RL) imaging. Upon X-ray irradiation, the nMOFs display sharp tunable emission peaks that span the visible to near-infrared spectral region (âŒ400â700 nm) based on the identity of the metal (Eu, Tb, or Eu/Tb). Surface modification of the nMOFs with polyethylene glycol (PEG) resulted in nanoparticles with enhanced aqueous stability that demonstrated both cyto- and hemo-compatibility important prerequisites for biological applications. Importantly, this is the first report to document and investigate the radioluminescent properties of lanthanide nMOFs. Taken together, the observed radioluminescent properties and low in vitro toxicity demonstrated by the nMOFs render them promising candidates for in vivo translation
Multicellular spheroids as in vitro models of oxygen depletion during FLASH irradiation
Purpose
The differential response of normal and tumor tissues to ultra-high dose rate radiation (FLASH) has raised new hope for treating solid tumors but, to date, the mechanism remains elusive. One leading hypothesis is that FLASH radiochemically depletes oxygen from irradiated tissues faster than it is replenished through diffusion. The purpose of this study is to investigate these effects within hypoxic multicellular tumor spheroids, through simulations and experiments.
Materials and Methods
Physicobiological equations were derived to model (i) the diffusion and metabolism of oxygen within spheroids; (ii) its depletion through reactions involving radiation-induced radicals; and (iii) the increase in radioresistance of spheroids, modeled according to the classical oxygen enhancement ratio and linear-quadratic response. These predictions were then tested experimentally in A549 spheroids exposed to electron irradiation at conventional (0.075 Gy/s) or FLASH (90 Gy/s) dose rates. Clonogenic survival, cell viability, and spheroid growth were scored post-radiation. Clonogenic survival of two other cell lines was also investigated.
Results
The existence of a hypoxic core in unirradiated tumor spheroids is predicted by simulations and visualized by fluorescence microscopy. Upon FLASH irradiation, this hypoxic core transiently expands, engulfing a large number of well-oxygenated cells. In contrast, oxygen is steadily replenished during slower conventional irradiation. Experimentally, clonogenic survival was around 3-fold higher in FLASH-irradiated spheroid compared to conventional irradiation, but no significant difference was observed for well-oxygenated 2D-cultured cells. This differential survival is consistent with the predictions of the computational model. FLASH irradiation of spheroids resulted in a dose-modifying factor of around 1.3 for doses above 10 Gy.
Conclusion
Tumor spheroids can be used as a model to study FLASH irradiation in vitro . The improved survival of tumor spheroids receiving FLASH radiation confirms that ultra-fast radiochemical oxygen depletion and its slow replenishment are critical components of the FLASH effect
Charge-Driven Fluorescence Blinking in Carbon Nanodots
This study focuses
on the mechanism of fluorescence blinking of
single carbon nanodots, which is one of their key but less understood
properties. The results of our single-particle fluorescence study
show that the mechanism of carbon nanodots blinking has remarkable
similarities with that of semiconductor quantum dots. In particular,
the temporal behavior of carbon nanodot blinking follows a power law
both at room and at cryogenic temperatures. Our experimental data
suggest that static quenching via Dexter-type electron transfer between
surface groups of a nanoparticle plays a major role in the transition
of carbon nanodots to off or gray states, whereas the transition back
to on states is governed by an electron tunneling from the particleâs
core. These findings advance our understanding of the complex mechanism
of carbon nanodots emission, which is one of the key steps for their
application in fluorescence imaging