The May 19, 2006 issue of Science included a paper by Holt et al.1 on “Fast Mass Transport Through Sub‐2‐Nanometer Carbon Nanotubes”. The paper was also featured on the cover, showing methane ...molecules translating inside a carbon nanotube (CNT). The authors explained how they prepared 2–6‐μm thin membranes consisting of double‐walled carbon nanotubes (DWNTs) all aligned perpendicular to the apparent membrane surface. These tubes are open at both ends and the space between the tubes is filled with dense Si3N4. Pure gas and water fluxes were measured at room temperature with the application of a small pressure difference. Interpretation of the results led to the conclusion that the membranes showed much higher fluxes than what was estimated from Knudsen gas diffusion and Poiseuille viscous flow models. The membranes have a straight‐channel morphology with a narrow pore‐size distribution and exceptionally smooth pore walls. The unusual geometry and surface properties make it difficult to compare the membrane’s properties with common membranes but there is no question that the mass transport in the aligned DWNTs is fast indeed. To appreciate how fast, we will consider their transport properties starting from the perspective of “conventional” porous membrane technology. Recent molecular dynamics simulations suggest that none of the classic models for gas (Knudsen) and water (Poiseuille) permeation work in a meaningful way for these nanotube membranes, and new models are needed.
Down the tubes: A recent article in the journal Science considered the gas‐ and liquid‐transport properties of carbon nanotubes (CNTs). Transport is indeed fast but separation is primarily by size exclusion. Here, recent molecular dynamics simulations are discussed, which suggest that none of the classic transport models are applicable for CNT membranes, and new models are needed. The formation of water chains in a CNT can be analogized by a train passing through a tunnel (see cartoon).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Thin, supported inorganic mesoporous membranes are used for the removal of salts, small molecules (PFAS, dyes, and polyanions) and particulate species (oil droplets) from aqueous sources with high ...flux and selectivity. Nanofiltration membranes can reject simple salts with 80-100% selectivity through a space charge mechanism. Rejection by size selectivity can be near 100% since the membranes can have a very narrow size distribution. Mesoporous membranes have received particular interest due to their (potential) stability under operational conditions and during defouling operations. More recently, membranes with extreme stability became interesting with the advent of in situ fouling mitigation by means of ultrasound emitted from within the membrane structure. For this reason, we explored the stability of available and new membranes with accelerated lifetime tests in aqueous solutions at various temperatures and pH values. Of the available ceria, titania, and magnetite membranes, none were actually stable under all test conditions. In earlier work, it was established that mesoporous alumina membranes have very poor stability. A new nanofiltration membrane was made of cubic zirconia membranes that exhibited near-perfect stability. A new ultrafiltration membrane was made of amorphous silica that was fully stable in ultrapure water at 80 °C. This work provides details of membrane synthesis, stability characterization and data and their interpretation.
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► PDMS can be easily applied as thin films on top of inorganic membranes. ► PDMS modification of inorganic membranes significantly improves gas selectivity. ► Defect flow is reduced due to filling of ...defects with PDMS. ► Modification can improve selectivity over a wide range of defect area fractions.
Simple, fast, and cost-effective defect abatement of inorganic gas separation membranes can be achieved by application of a continuous polymer layer. This polymer diminishes defect flow and is stable at a wide range of operating conditions. In the studies presented a thin layer of polydimethyl siloxane (PDMS) was applied to defective microporous silica and zeolite Y membranes. After application of PDMS, the H
2/CO
2 and CO
2/N
2 binary gas separation performance of both silica and zeolite membranes was found to improve significantly due to reduction in defect flow. At 30
°C, CO
2 selectivity of the silica membrane for a 1:1 CO
2/N
2 mixture improved from 1.5 to 835 after application of PDMS. At higher temperatures, N
2 in the permeate could no longer be detected by gas chromatography, which translated into a selectivity of >1000. There was also an improvement in the selectivity for a 1:1 H
2/CO
2 mixture at 30
°C from 1.9 without, to 66 with PDMS modification. Similar effects were found for supported zeolite Y membranes. The selectivity at 30
°C of a zeolite Y membrane for a 1:1 CO
2/N
2 mixture was found to increase from ∼0.93 before, to >1000 at 30
°C after modification with PDMS. Along with the improved separation factors, a reduction in the overall permeance occurred due to reduced defect flow contributions. The H
2 permeance at 130
°C decreased from 8.5
×
10
−8
mol/(m
2
s
Pa) for the uncoated silica membrane to 6.6
×
10
−9
mol/(m
2
s
Pa) after PDMS application. The CO
2 and N
2 permeance values at 130
°C, however, decreased by almost two orders of magnitude. The decrease in overall permeance due to defect abatement is supported by transport calculations assuming simple expressions for solution-diffusion through the membrane and Knudsen flow through the defects. These calculations show that the application of PDMS leads to a decrease in the overall permeance but an increase in the H
2 selectivity for a wide range of defect area fractions (<10
−4).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
▶ Rapid thermal processing (RTP) greatly reduces thermal treatment time of thin inorganic membranes. ▶ RTP results in finer microstructures and more densification. ▶ RTP does not adversely affect ...membrane integrity. ▶ RTP of supported γ-alumina membranes resulted in similar or better nanofiltration properties.
Rapid thermal processing (RTP) methods can be used to majorly reduce the processing time of thin supported inorganic membrane layers. The methods result in a finer, more homogeneous membrane microstructure and can be used to form membrane layers requiring high-temperature processing on supports with limited thermal stability. The short processing time of RTP reduces fabrication cost price, helps improve process optimization, and also encourages exploration of other multi-layer structures. The work in this paper demonstrates the use of RTP for thin defect-free supported mesoporous γ-alumina membranes that have a thickness of ∼400
nm. Conventionally thermal processed (CTP) and RTP γ-alumina membranes were characterized by ellipsometry, microscopy, aqueous ion rejection and permporometry. CTP and RTP membranes showed an aqueous ion rejection of >95% and >97%, respectively for a solution of 1
mol/m
3 calcium chloride dihydrate with 0.01
mol/m
3 aluminum chloride. According to ellipsometry analysis, the porosity of the RTP and CTP membranes are approximately 43 and 50%, respectively. Permporometry provides RTP and CTP membrane pore size, Ø
p of 3.4
+
2
t and 4.3
+
2
t
nm, respectively where
t
≈
0.35
nm.
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A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb
of
... TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons.
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A
bstract
This paper presents a search for direct electroweak gaugino or gluino pair production with a chargino nearly mass-degenerate with a stable neutralino. It is based on an integrated ...luminosity of 36.1 fb
−1
of
pp
collisions at
s
=
13
TeV collected by the ATLAS experiment at the LHC. The final state of interest is a disappearing track accompanied by at least one jet with high transverse momentum from initial-state radiation or by four jets from the gluino decay chain. The use of short track segments reconstructed from the innermost tracking layers significantly improves the sensitivity to short chargino lifetimes. The results are found to be consistent with Standard Model predictions. Exclusion limits are set at 95% confidence level on the mass of charginos and gluinos for different chargino lifetimes. For a pure wino with a lifetime of about 0.2 ns, chargino masses up to 460 GeV are excluded. For the strong production channel, gluino masses up to 1.65 TeV are excluded assuming a chargino mass of 460 GeV and lifetime of 0.2 ns.
A
bstract
A search for pair production of a scalar partner of the top quark in events with four or more jets plus missing transverse momentum is presented. An analysis of 36.1 fb
−1
of
s
=
13
TeV ...proton-proton collisions collected using the ATLAS detector at the LHC yields no significant excess over the expected Standard Model background. To interpret the results a simplified supersymmetric model is used where the top squark is assumed to decay via
t
˜
1
→
t
∗
χ
˜
1
0
and
t
˜
1
→
b
χ
˜
1
±
→
b
W
∗
χ
˜
1
0
, where χ
1
0
(χ
1
±
) denotes the lightest neutralino (chargino). Exclusion limits are placed in terms of the top-squark and neutralino masses. Assuming a branching ratio of 100% to
t
χ
˜
1
0
, top-squark masses in the range 450–1000 GeV are excluded for
χ
˜
1
0
masses below 160 GeV. In the case where
m
t
˜
1
∼
m
t
+
m
χ
˜
1
0
, top-squark masses in the range 235–590 GeV are excluded.
A
bstract
The coupling properties of the Higgs boson are studied in the four-lepton (
e
,
μ
) decay channel using 36.1 fb
−1
of
pp
collision data from the LHC at a centre-of-mass energy of 13 TeV ...collected by the ATLAS detector. Cross sections are measured for the main production modes in several exclusive regions of the Higgs boson production phase space and are interpreted in terms of coupling modifiers. The inclusive cross section times branching ratio for
H
→
ZZ
∗
decay and for a Higgs boson absolute rapidity below 2.5 is measured to be 1. 73
− 0.23
+ 0.24
(stat.)
− 0.08
+ 0.10
(exp.) ± 0.04(th.) pb compared to the Standard Model prediction of 1
.
34±0
.
09 pb. In addition, the tensor structure of the Higgs boson couplings is studied using an effective Lagrangian approach for the description of interactions beyond the Standard Model. Constraints are placed on the non-Standard-Model CP-even and CP-odd couplings to
Z
bosons and on the CP-odd coupling to gluons.
The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector using proton–proton collision data with a centre-of-mass energy of
s
=
7
TeV ...corresponding to an integrated luminosity of
4.7
fb
-
1
. Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-
k
t
algorithm with distance parameters
R
=
0.4
or
R
=
0.6
, and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a reference object such as a photon or a
Z
boson, for
20
≤
p
T
jet
<
1000
GeV
and pseudorapidities
|
η
|
<
4.5
. The effect of multiple proton–proton interactions is corrected for, and an uncertainty is evaluated using in situ techniques. The smallest JES uncertainty of less than 1 % is found in the central calorimeter region (
|
η
|
<
1.2
) for jets with
55
≤
p
T
jet
<
500
GeV
. For central jets at lower
p
T
, the uncertainty is about 3 %. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in proton–proton collisions and test-beam data, which also provide the estimate for
p
T
jet
>
1
TeV. The calibration of forward jets is derived from dijet
p
T
balance measurements. The resulting uncertainty reaches its largest value of 6 % for low-
p
T
jets at
|
η
|
=
4.5
. Additional JES uncertainties due to specific event topologies, such as close-by jets or selections of event samples with an enhanced content of jets originating from light quarks or gluons, are also discussed. The magnitude of these uncertainties depends on the event sample used in a given physics analysis, but typically amounts to 0.5–3 %.
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A
bstract
Inclusive jet and dijet cross-sections are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses a dataset with an integrated luminosity of 3.2 fb
...−1
recorded in 2015 with the ATLAS detector at the Large Hadron Collider. Jets are identified using the anti-
k
t
algorithm with a radius parameter value of
R
= 0
.
4. The inclusive jet cross-sections are measured double-differentially as a function of the jet transverse momentum, covering the range from 100 GeV to 3.5 TeV, and the absolute jet rapidity up to |
y
| = 3. The double-differential dijet production cross-sections are presented as a function of the dijet mass, covering the range from 300 GeV to 9 TeV, and the half absolute rapidity separation between the two leading jets within |
y
|
<
3,
y
∗
, up to
y
∗
= 3. Next-to-leading-order, and next-to-next-to-leading-order for the inclusive jet measurement, perturbative QCD calculations corrected for non-perturbative and electroweak effects are compared to the measured cross-sections.
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