Automatic Search Intervals for the Smoothing Parameter in Penalized Splines

The selection of smoothing parameter is central to the estimation of penalized splines. The best value of the smoothing parameter is often the one that optimizes a smoothness selection criterion, such as generalized cross-validation error (GCV) and restricted likelihood (REML). To correctly identify the global optimum rather than being trapped in an undesired local optimum, grid search is recommended for optimization. Unfortunately, the grid search method requires a pre-specified search interval that contains the unknown global optimum, yet no guideline is available for providing this interval. As a result, practitioners have to find it by trial and error. To overcome such difficulty, we develop novel algorithms to automatically find this interval. Our automatic search interval has four advantages. (i) It specifies a smoothing parameter range where the associated penalized least squares problem is numerically solvable. (ii) It is criterion-independent so that different criteria, such as GCV and REML, can be explored on the same parameter range. (iii) It is sufficiently wide to contain the global optimum of any criterion, so that for example, the global minimum of GCV and the global maximum of REML can both be identified. (iv) It is computationally cheap compared with the grid search itself, carrying no extra computational burden in practice. Our method is ready to use through our recently developed R package gps (>= version 1.1). It may be embedded in more advanced statistical modeling methods that rely on penalized splines.Comment: R code is available at https://github.com/ZheyuanLi/gps-vignettes/blob/main/gps2.pd

Cryptanalysis and improvement of an efficient certificateless signature scheme

In traditional digital signature schemes, certificates signed by a trusted party are required to ensure the authenticity of the public key. In Asiacrypt 2003, the concept of certificateless signature scheme was introduced. The advantage of certificate-less public key cryptography successfully eliminates the necessity of certificates in the traditional public key cryptography and simultaneously solves the inherent key escrow problem suffered in identity-based cryptography. Recently, Yap et al. proposed an efficient certificateless signature scheme and claimed that their scheme is existentially unforgeable in the random oracle model. In this paper, we show that the certificateless signature scheme proposed by Yap et al. is insecure against public key replacement attacks. Furthermore, we propose an improved certificateless signature scheme, which is existentially unforgeable against adaptive chosen message attacks under the computational Diffie-Hellman assumption in the random oracle model and provide the security proof of the proposed scheme

An Efficient Certificate-Based Designated Verifier Signature Scheme

Certificate-based public key cryptography not only solves certificate revocation problem in traditional PKI but also overcomes key escrow problem inherent in identity-based cryptosystems. This new primitive has become an attractive cryptographic paradigm. In this paper, we propose the notion and the security model of certificate-based designated verifier signatures (CBDVS). We provide the first construction of CBDVS and prove that our scheme is existentially unforgeable against adaptive chosen message attacks in the random oracle model. Our scheme only needs two pairing operations, and the signature is only one element in the bilinear group G1. To the best of our knowledge, our scheme enjoys shortest signature length with less operation cost

Certificate-Based Signcryption: Security Model and Efficient Construction

Signcryption is an important cryptographic primitive that simultaneously achieves confidentiality and authentication in an efficient manner. In 2008, Luo et al. introduced the notion of certificate-based signcryption and proposed the first construction of certificate-based signcryption. However, their scheme is insecure under the key replacement attack and also does not provide insider security. To overcome these disadvantages, we introduce a strengthened security model of certificate-based signcryption in this paper. The new security model accurately models insider security and the key replacement attacks that might be attempted by an adversary in a real certificate-based signcryption system. We also propose a new certificate-based signcryption scheme that reaches insider security and resists key replacement attacks. We show that this scheme is both chosen-ciphertext secure and existentially unforgeable in the random oracle model. Furthermore, performance analysis shows that the proposed scheme is efficient and practical

Cryptanalysis and improvement of certificateless aggregate signature with conditional privacy-preserving for vehicular sensor networks

Secure aggregate signature schemes have attracted more concern due to their wide application in resource constrained environment. Recently, Horng et al. [S. J. Horng et al., An efficient certificateless aggregate signature with conditional privacy-preserving for vehicular sensor networks, Information Sciences 317 (2015) 48-66] proposed an efficient certificateless aggregate signature with conditional privacy-preserving for vehicular sensor networks. They claimed that their scheme was provably secure against existential forgery on adaptively chosen message attack in the random oracle model. In this paper, we show that their scheme is insecure against a malicious-but-passive KGC under existing security model. Further, we propose an improved certificateless aggregate signature

Effect of Cr3C2 Content on the Microstructure and Wear Resistance of Fe3Al/Cr3C2 Composites

In this paper, an engine piston ring coating comprising composite material of Fe3Al and Cr3C2 mixed powder was prepared by laser cladding onto carbon structural steel. The microstructure and tribological properties of the cladding materials were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and wear tests. The influence mechanism of the Cr3C2 content in cladding powder was studied. During the process of wear, the soft Fe3Al/Fe2AlCr matrix is first ground off, and the hard Cr7C3 phase initially supports the abrasive surface before being worn away into hard particles, resulting in abrasive wear. With the increase in Cr3C2 content, the hardness of the cladding layer increases, the proportion of the Cr7C3 phase increases, and the morphology changes from a sparse network to a dense floccule. Of the cladding layers with different Cr3C2 content, the 15 wt.% Cr3C2 cladding layer had the lowest friction coefficient, and the 25 wt.% Cr3C2 cladding layer had the lowest wear rate. The low wear rate of the 25 wt.% Cr3C2 cladding layer can be attributed to the fact that adhesive wear does not easily occur and the fine microstructure of the strengthening phase, which facilitates better separation in the grinding surfaces

ELECTROMAGNETIC SELF-LOCKING DEVICE FOR AIR CYLINDERS IN SPENT FUEL STORAGE SYSTEM OF PEBBLE-BED HIGH TEMPERATURE GAS-COOLED REACTOR

ABSTRACT In the spent fuel storage system of pebble-bed high temperature gas-cooled reactor, several air cylinders would be employed in complex machines, such as the spent fuel charging apparatus and the spent fuel canister crane. The cylinders were designed to actuate movements smoothly in radioactive environment. In order to lock them in safe position when the compressed air source is offline by accident, an electromagnetic self-locking device was designed. When power-off, the compressive spring would push out the lock plunger to enable self-lock. When power-on, the lock plunger would be withdrawn by the magnetic force of the coil to unlock the cylinder. In order to optimize the design more efficiently, numerical simulation was performed to optimize geometry parameters of the structure surrounding the working air gap so as to improve the performance of the device. A prototype was then fabricated. Combining the simulation results with experimental test, the actuating force characteristics of the device in locking and unlocking process was analyzed. The temperature rise when the device stays unlocked with power supply was also calculated and validated. The results showed that this electromagnetic selflocking device could realize the locking and unlocking functions effectively, and the maximum temperature rise also conforms the required limit. The as-fabricated device would help guarantee the fail-safe feature of the air cylinders of complex machines in compressed air outage