1,497 research outputs found
Inexact proximal methods for weakly convex functions
This paper proposes and develops inexact proximal methods for finding
stationary points of the sum of a smooth function and a nonsmooth weakly convex
one, where an error is present in the calculation of the proximal mapping of
the nonsmooth term. A general framework for finding zeros of a continuous
mapping is derived from our previous paper on this subject to establish
convergence properties of the inexact proximal point method when the smooth
term is vanished and of the inexact proximal gradient method when the smooth
term satisfies a descent condition. The inexact proximal point method achieves
global convergence with constructive convergence rates when the Moreau envelope
of the objective function satisfies the Kurdyka-Lojasiewicz (KL) property.
Meanwhile, when the smooth term is twice continuously differentiable with a
Lipschitz continuous gradient and a differentiable approximation of the
objective function satisfies the KL property, the inexact proximal gradient
method achieves the global convergence of iterates with constructive
convergence rates.Comment: 26 pages, 3 table
ĐẶC ĐIỂM ĐỊA HÌNH ĐÁY VÀ TRẦM TÍCH TẦNG MẶT VÙNG BIỂN QUẦN ĐẢO THỔ CHU
Tho Chu archipelago was formed by sedimentary rocks (176 metres in height) with horizontal position. The islands are limited by the abraded slopes and landslide disruption. The shoreline morphology is cliffs, abrasion and boulders with good size, low abrasion, and little change. Vegetation of island is still in the primary condition. The average depth of Tho Chu archipelago is about 20 - 30 m with canyons of -96 m and several underwater hills which are covered by coral reefs. The characteristics of seabed sediment are mostly kinds of coarse - grained sediments such as gravelly sand (gS), slightly gravelly muddy sand ((g)mS), muddy sand (mS), mud (M).Quần đảo Thổ Chu được cấu tạo bởi các đá trầm tích (cao 176 m), có thế nằm ngang. Xung quanh đảo được giới hạn các sườn dốc mài mòn và đỗ vỡ sụp lở. Hình thái đường bờ là các vách dốc, mài mòn và các tảng lăn với kích thước khá lớn, bị mài mòn yếu, ít bị thay đổi, thảm thực vật trên đảo còn nguyên sinh. Độ sâu trung bình quần đảo Thổ Chu khoảng 20 - 30 m, có rãnh sâu có độ sâu -96 m và có rất nhiều đồi ngầm phần lớn được phủ san hô. Đặc điểm trầm tích tầng mặt được phủ bởi các kiểu trầm tích hạt thô: Cát chứa graven, cát chứa bùn sét (và graven), cát chứa bùn sét, bùn sét
DEVELOPMENT AND EVALUATION OF ORAL SUSTAINED-RELEASE RANITIDINE DELIVERY SYSTEM BASED ON BACTERIAL NANOCELLULOSE MATERIAL PRODUCED BY KOMAGATAEIBACTER XYLINUS
Objective: The short biological half-life (2-3 h) and low bioavailability (50 %) of ranitidine (RAN) following oral administration favor the development of a controlled release system. This study was aimed to develop and in vitro evaluate oral sustained-release RAN delivery system based on the bacterial nanocellulose material (BNM) produced by Komagataeibacter xylinus (K. xylinus) from selected culture media.
Methods: BNMs are biosynthesized by K. xylinus in the standard medium (SM) and coconut water (CW). RAN was loaded in BNMs by the absorption method. The structural and physicochemical properties of BNMs and BNMs-RAN were evaluated via swelling behavior, FTIR, and FESEM techniques. Moreover, the effect of BNMs on RAN release profile and release kinetics was analyzed and evaluated.
Results: The amount of loaded RAN or entrapment efficacy for BNM-CW is higher than for BNM-SM. The BNM-SM-RAN and BNM-CW-RAN exhibited a decreased initial burst release system followed by a prolonged RAN release up to 24 h in relation to the commercial tablets containing RAN. The RAN release from these formulations was found higher in the SGF medium than that of in SIF medium. RAN released from these formulations was found to follow the Korsmeyer-Peppas model and diffusion sustained drug release mechanism. The sustained release of RAN from BNM-SM-RAN was slower than for RAN from BNM-CW-RAN, but the mechanism of sustained RAN release was the same.
Conclusion: Oral sustained-release RAN delivery system based on BNMs was successfully prepared and evaluated for various in vitro parameters. The biopolymers like BNM-SM and BNM-CW could be utilized to develop oral sustained RAN release dosage form
Inexact reduced gradient methods in smooth nonconvex optimization
This paper proposes and develops new line search methods with inexact
gradient information for finding stationary points of nonconvex continuously
differentiable functions on finite-dimensional spaces. Some abstract
convergence results for a broad class of line search methods are reviewed and
extended. A general scheme for inexact reduced gradient (IRG) methods with
different stepsize selections are proposed to construct sequences of iterates
with stationary accumulation points. Convergence results with convergence rates
for the developed IRG methods are established under the Kurdyka-Lojasiewicz
property. The conducted numerical experiments confirm the efficiency of the
proposed algorithms
Globally Convergent Coderivative-Based Generalized Newton Methods in Nonsmooth Optimization
This paper proposes and justifies two globally convergent Newton-type methods
to solve unconstrained and constrained problems of nonsmooth optimization by
using tools of variational analysis and generalized differentiation. Both
methods are coderivative-based and employ generalized Hessians (coderivatives
of subgradient mappings) associated with objective functions, which are either
of class , or are represented in the form of convex
composite optimization, where one of the terms may be extended-real-valued. The
proposed globally convergent algorithms are of two types. The first one extends
the damped Newton method and requires positive-definiteness of the generalized
Hessians for its well-posedness and efficient performance, while the other
algorithm is of {the regularized Newton type} being well-defined when the
generalized Hessians are merely positive-semidefinite. The obtained convergence
rates for both methods are at least linear, but become superlinear under the
semismooth property of subgradient mappings. Problems of convex composite
optimization are investigated with and without the strong convexity assumption
{on smooth parts} of objective functions by implementing the machinery of
forward-backward envelopes. Numerical experiments are conducted for Lasso
problems and for box constrained quadratic programs with providing performance
comparisons of the new algorithms and some other first-order and second-order
methods that are highly recognized in nonsmooth optimization.Comment: arXiv admin note: text overlap with arXiv:2101.1055
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