114 research outputs found
Multifunctional Nanocomposites based on Bacterial Cellulose
Cellulose is biodegradable, renewable, and abundant in nature thus cellulose (or paper)-based products can be inexpensively produced and recycled. Among cellulosic materials, bacterial nanocellulose (BNC) draws a special research attention due to the inherent three-dimensional nanofibrous structure, excellent mechanical flexibility, high purity and well-defined surface chemistry, and cost-efficient, scalable and environment-friendly synthesis. BNC can be biosynthesized by Gluconacetobacter xylinus, which is the most characterized BNC producer among various microorganisms. BNC is composed of highly pure cellulose nanofibrils, produced from well-defined dextrose through biochemical steps and subsequent self-assembling of the secreted cellulose fibrils which has the dimension ranges from 25 to 100 nm in diameter from bacteria in the culture medium. During the biosynthesis of BNC, shape-controlled hydrogels with well-defined network structure pore diameters below 10 µm can be easily achieved. For all the above-mentioned reasons, BNC is a highly promising platform material for the fabrication of functional composites through in situ growth or adsorption of pre-synthesized nanostructures on the nanoscale cellulose fibers.
In this work, we have designed and demonstrated novel strategies to realize BNC-based functional nanocomposites with applications in sensing, water purification and energy storage. We have demonstrated a BNC film-based surface enhanced Raman scattering (SERS) substrate which has 3D porous structure and ultrafine fibers with uniform and dense adsorption of plasmonic nanostructures, resulting large SERS enhancement and excellent uniformity of SERS activity.
For the first time, we have demonstrated a novel, highly scalable, cost-effective and green strategy to realize functional BNC-based foams/membranes. Functional materials such as graphene oxide (GO), polydopamine (PDA) can be efficiently incorporated within BNC matrix during its growth. Owing to the intercalation of functional materials within the layered BNC matrix, the functional composites showed excellent mechanical robustness and flexibility, which is crucial for efficient, large-scale applications, either as a foam or as a membrane.
Specifically, we have designed and developed a bilayered hybrid biofoam comprised of BNC and RGO and a completely biodegradable bilayered foam based on BNC and PDA for highly efficient solar steam generation, which can be a sustainable solution to alleviate global water crisis. An innovative water filtration membrane based on BNC and RGO which harvests sunlight to kill microorganisms has been developed to provide a novel anti-biofouling approach. We have also demonstrated a robust filtration membrane based on BNC loaded with GO and PdNPs, which exhibited excellent dye degradation performance for highly efficient wastewater treatment. Furthermore, the in situ fabrication approach has been extended to polymeric materials such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to realize hybrid flexible supercapacitor electrodes based on RGO, BNC and PEDOT:PSS.
The fabrication strategies and materials design demonstrated in this work can be easily extended to realize various BNC-based nanocomposites with applications in water purification, energy harvesting, sensing, catalysis, and life sciences
Multifunctional Nanocomposites based on Bacterial Cellulose
Cellulose is biodegradable, renewable, and abundant in nature thus cellulose (or paper)-based products can be inexpensively produced and recycled. Among cellulosic materials, bacterial nanocellulose (BNC) draws a special research attention due to the inherent three-dimensional nanofibrous structure, excellent mechanical flexibility, high purity and well-defined surface chemistry, and cost-efficient, scalable and environment-friendly synthesis. BNC can be biosynthesized by Gluconacetobacter xylinus, which is the most characterized BNC producer among various microorganisms. BNC is composed of highly pure cellulose nanofibrils, produced from well-defined dextrose through biochemical steps and subsequent self-assembling of the secreted cellulose fibrils which has the dimension ranges from 25 to 100 nm in diameter from bacteria in the culture medium. During the biosynthesis of BNC, shape-controlled hydrogels with well-defined network structure pore diameters below 10 µm can be easily achieved. For all the above-mentioned reasons, BNC is a highly promising platform material for the fabrication of functional composites through in situ growth or adsorption of pre-synthesized nanostructures on the nanoscale cellulose fibers.
In this work, we have designed and demonstrated novel strategies to realize BNC-based functional nanocomposites with applications in sensing, water purification and energy storage. We have demonstrated a BNC film-based surface enhanced Raman scattering (SERS) substrate which has 3D porous structure and ultrafine fibers with uniform and dense adsorption of plasmonic nanostructures, resulting large SERS enhancement and excellent uniformity of SERS activity.
For the first time, we have demonstrated a novel, highly scalable, cost-effective and green strategy to realize functional BNC-based foams/membranes. Functional materials such as graphene oxide (GO), polydopamine (PDA) can be efficiently incorporated within BNC matrix during its growth. Owing to the intercalation of functional materials within the layered BNC matrix, the functional composites showed excellent mechanical robustness and flexibility, which is crucial for efficient, large-scale applications, either as a foam or as a membrane.
Specifically, we have designed and developed a bilayered hybrid biofoam comprised of BNC and RGO and a completely biodegradable bilayered foam based on BNC and PDA for highly efficient solar steam generation, which can be a sustainable solution to alleviate global water crisis. An innovative water filtration membrane based on BNC and RGO which harvests sunlight to kill microorganisms has been developed to provide a novel anti-biofouling approach. We have also demonstrated a robust filtration membrane based on BNC loaded with GO and PdNPs, which exhibited excellent dye degradation performance for highly efficient wastewater treatment. Furthermore, the in situ fabrication approach has been extended to polymeric materials such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to realize hybrid flexible supercapacitor electrodes based on RGO, BNC and PEDOT:PSS.
The fabrication strategies and materials design demonstrated in this work can be easily extended to realize various BNC-based nanocomposites with applications in water purification, energy harvesting, sensing, catalysis, and life sciences
Sync+Sync: A Covert Channel Built on fsync with Storage
Scientists have built a variety of covert channels for secretive information
transmission with CPU cache and main memory. In this paper, we turn to a lower
level in the memory hierarchy, i.e., persistent storage. Most programs store
intermediate or eventual results in the form of files and some of them call
fsync to synchronously persist a file with storage device for orderly
persistence. Our quantitative study shows that one program would undergo
significantly longer response time for fsync call if the other program is
concurrently calling fsync, although they do not share any data. We further
find that, concurrent fsync calls contend at multiple levels of storage stack
due to sharing software structures (e.g., Ext4's journal) and hardware
resources (e.g., disk's I/O dispatch queue).
We accordingly build a covert channel named Sync+Sync. Sync+Sync delivers a
transmission bandwidth of 20,000 bits per second at an error rate of about
0.40% with an ordinary solid-state drive. Sync+Sync can be conducted in
cross-disk partition, cross-file system, cross-container, cross-virtual
machine, and even cross-disk drive fashions, without sharing data between
programs. Next, we launch side-channel attacks with Sync+Sync and manage to
precisely detect operations of a victim database (e.g., insert/update and
B-Tree node split). We also leverage Sync+Sync to distinguish applications and
websites with high accuracy by detecting and analyzing their fsync frequencies
and flushed data volumes. These attacks are useful to support further
fine-grained information leakage.Comment: A full version for the paper with the same title accepted by the 33rd
USENIX Security Symposium (USENIX Security 2024
Speaker verification using attentive multi-scale convolutional recurrent network
In this paper, we propose a speaker verification method by an Attentive
Multi-scale Convolutional Recurrent Network (AMCRN). The proposed AMCRN can
acquire both local spatial information and global sequential information from
the input speech recordings. In the proposed method, logarithm Mel spectrum is
extracted from each speech recording and then fed to the proposed AMCRN for
learning speaker embedding. Afterwards, the learned speaker embedding is fed to
the back-end classifier (such as cosine similarity metric) for scoring in the
testing stage. The proposed method is compared with state-of-the-art methods
for speaker verification. Experimental data are three public datasets that are
selected from two large-scale speech corpora (VoxCeleb1 and VoxCeleb2).
Experimental results show that our method exceeds baseline methods in terms of
equal error rate and minimal detection cost function, and has advantages over
most of baseline methods in terms of computational complexity and memory
requirement. In addition, our method generalizes well across truncated speech
segments with different durations, and the speaker embedding learned by the
proposed AMCRN has stronger generalization ability across two back-end
classifiers.Comment: 21 pages, 6 figures, 8 tables. Accepted for publication in Applied
Soft Computin
Observation of superconductivity in the noncentrosymmetric nodal chain semimetal Ba5In4Bi5
The combination with superconductivity and topological nontrivial band
structure provides a promising route towards novel quantum states such as
topological superconductivity. Here, we report the first observation of
superconductivity (4.1 K) in Ba5In4Bi5 single crystal, a noncentrosymmetric
topological semimetal featuring nodal chain loops at the high-symmetry points R
and X. The magnetization, resistivity, and specific heat capacity measurements
reveal that Ba5In4Bi5 is a moderately coupled type-II Bardeen-Cooper-Schrieffer
superconductor. Bulk superconductivity is suggested from the magnetic
susceptibility and specific heat measurements. The results show that Ba5In4Bi5
provides a new platform for exploring the relationship of superconductivity and
topological nontrivial band topology
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