A Cipher Based on Prefix Codes Grošek, Otokar; Hromada, Viliam; Horák, Peter
Sensors,
09/2021, Letnik:
21, Številka:
18
Journal Article
Recenzirano
Odprti dostop
A prefix code, a P-code, is a code where no codeword is a prefix of another codeword. In this paper, a symmetric cipher based on prefix codes is proposed. The simplicity of the design makes this ...cipher usable for Internet of Things applications. Our goal is to investigate the security of this cipher. A detailed analysis of the fundamental properties of P-codes shows that the keyspace of the cipher is too large to mount a brute-force attack. Specifically, in this regard we will find bounds on the number of minimal P-codes containing a binary word given in advance. Furthermore, the statistical attack is difficult to mount on such cryptosystem due to the attacker’s lack of information about the actual words used in the substitution mapping. The results of a statistical analysis of possible keys are also presented. It turns out that the distribution of the number of minimal P-codes over all binary words of a fixed length is Gaussian.
On the Maximum Size of a Prefix Code Horak, Peter; Hromada, Viliam; Grosek, Otokar
IEEE transactions on information theory
69, Številka:
5
Journal Article
Recenzirano
Odprti dostop
A prefix code minimal with respect to a bitstring <inline-formula> <tex-math notation="LaTeX">x </tex-math></inline-formula> is a prefix code where <inline-formula> <tex-math notation="LaTeX">x ...</tex-math></inline-formula> is a concatenation of its codewords and it is minimal with respect to this property. What is the maximum size <inline-formula> <tex-math notation="LaTeX">M(n) </tex-math></inline-formula> among all minimal codes over all bitstrings of length <inline-formula> <tex-math notation="LaTeX">n? </tex-math></inline-formula> In this paper we determine the value of <inline-formula> <tex-math notation="LaTeX">M(n) </tex-math></inline-formula> for all natural numbers <inline-formula> <tex-math notation="LaTeX">n </tex-math></inline-formula>, discuss its computational complexity, relation to the Lambert function, provide tight upper bounds, and describe how the value of <inline-formula> <tex-math notation="LaTeX">M(n) </tex-math></inline-formula> enables one to construct efficiently a Huffman code in the case of uniform probability distribution of the codewords.
Abstract
Using an evolutionary algorithm combined with a gradient descent (GD) method we design optical cavities with significantly enhanced strong coupling rates between cavity photons and a single ...quantum emitter. Our approach allows us to find specially designed non-spherical mirrors which lead to high-finesse cavity eigenmodes with large field enhancement at the center of the cavity. The method is based on adding consecutive perturbations to an initial spherical mirror shape using the GD method for optimization. We present mirror profiles which demonstrate higher cavity cooperativity than any spherical cavity of the same size. Finally, we demonstrate numerically how such a cavity enhances the operation frequency and purity of coupling a Ca
+
ion to an optical fiber photon.
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High speed electrospinning (HSES), compatible with pharmaceutical industry, was used to demonstrate the viability of the preparation of drug-loaded polymer nanofibers with radically ...higher productivity than the known single-needle electrospinning (SNES) setup. Poorly water-soluble itraconazole (ITRA) was formulated with PVPVA64 matrix polymer using four different solvent-based methods such as HSES, SNES, spray drying (SD) and film casting (FC). The formulations were assessed in terms of improvement in the dissolution rate of ITRA (using a “tapped basket” dissolution configuration) and analysed by SEM, DSC and XRPD. Despite the significantly increased productivity of HSES, the obtained morphology was very similar to the SNES nanofibrous material. ITRA transformed into an amorphous form, according to the DSC and XRPD results, in most cases except the FC samples. The limited dissolution of crystalline ITRA could be highly improved: fast dissolution occurred (>90% within 10min) in the cases of both (the scaled-up and the single-needle) types of electrospun fibers, while the improvement in the dissolution rate of the spray-dried microspheres was significantly lower. Production of amorphous solid dispersions (ASDs) with the HSES system proved to be flexibly scalable and easy to integrate into a continuous pharmaceutical manufacturing line, which opens new routes for the development of industrially relevant nanopharmaceuticals.
We solve a system of generalized nonlinear Schrödinger equations to study the nonlinear dynamics of ultrashort pulse propagation in multimode fibers. Due to pulse walk-off, permanent intermodal power ...transfer between modes is observed even in absence of phase matching. The strength of intermodal effects is found to depend strongly on modal symmetries, which results in preferential coupling between the LP(0n) modes. The scaling of nonlinear multimode effects in large-core fibers for the generation of ultra-high power spectral density supercontinua is finally discussed.
Hypoxia induces rapid and dramatic changes in cellular metabolism, in part through inhibition of target of rapamycin (TOR) kinase complex 1 (TORC1) activity. Genetic studies have shown the tuberous ...sclerosis tumor suppressors TSC1/2 and the REDD1 protein to be essential for hypoxia regulation of TORC1 activity in Drosophila and in mammalian cells. The molecular mechanism and physiologic significance of this effect of hypoxia remain unknown. Here, we demonstrate that hypoxia and REDD1 suppress mammalian TORC1 (mTORC1) activity by releasing TSC2 from its growth factor-induced association with inhibitory 14-3-3 proteins. Endogenous REDD1 is required for both dissociation of endogenous TSC2/14-3-3 and inhibition of mTORC1 in response to hypoxia. REDD1 mutants that fail to bind 14-3-3 are defective in eliciting TSC2/14-3-3 dissociation and mTORC1 inhibition, while TSC2 mutants that do not bind 14-3-3 are inactive in hypoxia signaling to mTORC1. In vitro, loss of REDD1 signaling promotes proliferation and anchorage-independent growth under hypoxia through mTORC1 dysregulation. In vivo, REDD1 loss elicits tumorigenesis in a mouse model, and down-regulation of REDD1 is observed in a subset of human cancers. Together, these findings define a molecular mechanism of signal integration by TSC1/2 that provides insight into the ability of REDD1 to function in a hypoxia-dependent tumor suppressor pathway.
We present a novel refractometric sensor based on a coated all-coupling optical-fiber-nanowire microcoil resonator which is robust, compact, and comprises an intrinsic fluidic channel. We calculate ...the device sensitivity and find its dependence on the nanowire diameter and coating thickness. A sensitivity as high as 700 nm/RIU and a refractive index resolution as low as 10(-10) are predicted.
Abstract
We demonstrate the use of machine learning through convolutional neural networks to solve inverse design problems of optical resonator engineering. The neural network finds a harmonic ...modulation of a spherical mirror to generate a resonator mode with a given target topology (“mode on-demand”). The procedure allows us to optimize the shape of mirrors to achieve a significantly enhanced coupling strength and cooperativity between a resonator photon and a quantum emitter located at the center of the resonator. In a second example, a double-peak mode is designed which would enhance the interaction between two quantum emitters, e.g., for quantum information processing.
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