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Non-monotonic dependence of fluid dissipation on fluid density in fluid-coupled nanoresonators
No full textSpecific Ion and Electric Field Controlled Diverse Ion Distribution and Electroosmotic Transport in a Polyelectrolyte Brush Grafted Nanochannel
No full textControlling ion distribution inside a charged nanochannel
is central
to using such channels in diverse applications. Here, we show the
possibility of using a charged polyelectrolyte (PE) brush-grafted
nanochannel for triggering diverse nanoscopic ion distribution and
nanofluidic electroosmotic transport by controlling the valence and
size of the counterions (that screen the charges of the PE brushes)
and the strength of an externally applied axial electric field. We
atomistically simulate separate cases of fully charged polyacrylic
acid (PAA) brush functionalized nanochannels with Na+,
Cs+, Ca2+, Ba2+, and Y3+ counterions screening the PE charges. Four key findings emerge from
our simulations. First, we find that the counterions with a greater
valence and a smaller size prefer to remain localized inside the brush
layer. Second, for the case where there is an added chloride salt
with the same cation (as the screening counterions), there are more
coions (Cl– ions) in the brush-free bulk than counterions
(for counterions Na+, Ca2+, Ba2+,
Y3+): this is a manifestation of the overscreening (OS)
of the PE brush layer. Contrastingly, the number of Cs+ ions remain higher than the Cl– ions inside the
brush-free bulk, ensuring that there is no OS effect for this case.
Third, large applied electric field enables a few Na+,
Cs+, and Ba2+ counterions to leave the brush
layer and to go to the bulk: this makes the OS of the PE brush layer
disappear for the cases of PE brushes being screened by the Na+ and Ba2+ ions. On the other hand, no such electric-field-mediated
disappearance of OS is observed for the cases of Ca2+ and
Y3+ screening counterions; we attribute this to the firm
attachment of these counterions to the negatively charged monomers.
Free energy associated with a counterion binding to a PE chain corroborates
this diversity in the counterion-specific response to the applied
electric field. Finally, we demonstrate that such diverse ion distributions,
along with specific electric-field-strength-dependent ion properties,
lead to (1) electroosmotic (EOS) transport in nanochannels grafted
with PAA brushes screened with Cs+ ions to be always counterion
dominated, (2) EOS transport in nanochannels grafted with PAA brushes
screened with Ca2+ and Y3+ ions to be always
coion-dominated, and (3) EOS transport in nanochannels grafted with
PAA brushes screened with Na+ and Ba2+ ions
to be coion dominated for smaller electric fields and counterion dominated
for larger electric fields
Interplay of Local Heating, Nanoconfinement, and Tunable Liquid–Wall Interactions Drive Rapid Imbibition and Pronounced Mixing Between Two Immiscible Liquids
No full textDesigning novel and energy-efficient
strategies for disturbing
stable interfaces between two immiscible liquids hold the key for
a myriad of applications. In this Letter, we propose a highly effective
strategy where localized heating (costing less energy) of an interface
between two immiscible liquids confined in a nanochannel enable rapid
imbibition and mixing between these two liquids. The exact dynamics
(imbibition or mixing) depend on the relative wettability of these
two liquids to the nanochannel wall. For the case where one liquid
is philic and the other is phobic to the nanochannel wall, local heating
makes a particular liquid imbibe into the zone occupied by the other
liquid with the philic liquid occupying near-wall locations and the
phobic liquid occupying the bulk (far wall) positions. The extent
of imbibition is quantified in terms of the interfacial thickness
between the two liquids, which is found to be larger than the case
where the entire system is heated (costing greater energy). We further
show that this interfacial thickness can be enhanced by changing the
position (along the nanochannel) of localized heating. Finally, we
demonstrate that for the immiscible two liquid systems having identical
wetting interactions with the wall, the lack of preference of occupying
the near wall location by any of the liquids lead to their enhanced
mixing in the presence of the localized heating (that imparts additional
energy to the liquids enforcing them to cross over to the side of
the other liquid)
Quantification of Mono- and Multivalent Counterion-Mediated Bridging in Polyelectrolyte Brushes
No full textInterplay of Local Heating, Nanoconfinement, and Tunable Liquid–Wall Interactions Drive Rapid Imbibition and Pronounced Mixing Between Two Immiscible Liquids
No full textDesigning novel and energy-efficient
strategies for disturbing
stable interfaces between two immiscible liquids hold the key for
a myriad of applications. In this Letter, we propose a highly effective
strategy where localized heating (costing less energy) of an interface
between two immiscible liquids confined in a nanochannel enable rapid
imbibition and mixing between these two liquids. The exact dynamics
(imbibition or mixing) depend on the relative wettability of these
two liquids to the nanochannel wall. For the case where one liquid
is philic and the other is phobic to the nanochannel wall, local heating
makes a particular liquid imbibe into the zone occupied by the other
liquid with the philic liquid occupying near-wall locations and the
phobic liquid occupying the bulk (far wall) positions. The extent
of imbibition is quantified in terms of the interfacial thickness
between the two liquids, which is found to be larger than the case
where the entire system is heated (costing greater energy). We further
show that this interfacial thickness can be enhanced by changing the
position (along the nanochannel) of localized heating. Finally, we
demonstrate that for the immiscible two liquid systems having identical
wetting interactions with the wall, the lack of preference of occupying
the near wall location by any of the liquids lead to their enhanced
mixing in the presence of the localized heating (that imparts additional
energy to the liquids enforcing them to cross over to the side of
the other liquid)
Simultaneous Energy Generation and Flow Enhancement (Electroslippage Effect) in Polyelectrolyte Brush Functionalized Nanochannels
No full textEnergy
generation through nanofluidics is a topic of great nanotechnological
relevance. Here, we conduct all-atom molecular dynamics (MD) simulations
of the transport of water and ions in a pressure-driven flow in nanochannels
grafted with charged polyelectrolyte (PE) brushes and discover the
possibility of simultaneous electrokinetic energy generation and flow
enhancement (henceforth denoted as the electroslippage effect). Such PE-brush-functionalized nanochannels have been recently shown
to demonstrate an overscreening (OS) effect (characterized by the
presence of a greater number of screening counterions within the PE
brush layer than needed to screen the PE brush charges), a consequent
presence of excess co-ions within the PE brush-free bulk, and a co-ion-driven
electroosmotic (EOS) transport in the presence of small to moderate
applied axial electric fields. In this study, however, we find that
the streaming current, which represents the current generated by the
flow-driven downstream advection of the charge imbalance present within
the electric double layer (EDL) that screens the PE brush charges,
is governed by the migration of the counterions. This stems from the
fact that the highest contribution to the overall streaming current
arises from the region near the PE brush–water interface (where
there is an excess of counterions), while the brush-free bulk yields
a hitherto unreported, but small, co-ion-dictated streaming current.
This downstream advection of the charge imbalance (and the resultant
counterion-driven streaming current) eventually leads to the development
of an electric field (streaming electric field) in the direction that
is opposite the direction of the counterion-driven streaming current.
The streaming current and the streaming electric field interact to
generate the electrokinetic energy. Equally important, this streaming
electric field induces an EOS transport, which becomes co-ion-driven,
due to the presence of excess co-ions in the brush-free bulk. For
the case of nanochannels grafted with negatively charged PE brushes,
the streaming electric field will be in a direction that is opposite
that of the pressure-driven transport, and hence the co-ion (or anion)
driven EOS flow will be in the same direction as the pressure-driven
transport. On the other hand, for the case of nanochannels grafted
with positively charged PE brushes, the streaming electric field will
be in the same direction as the pressure-driven flow, and hence the
co-ion (or cation) driven EOS flow, will again be in the same direction
as the pressure-driven flow. Therefore, whenever there occurs a presence
of the OS and the resulting co-ion-driven EOS transport in PE brush
grafted nanochannels, regardless of the sign of the charges of the
PE brushes, this EOS transport will always aid the
pressure-driven transport and will cause the most fascinating increase
in the net volume flow rate across the nanochannel cross section,
which is the electroslippage effect
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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