# Search: authors:"Zhen-Hang Yang"

42 papers found.
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#### On converses of some comparison inequalities for homogeneous means

In this paper, the necessary and suffcient conditions for the converses of comparison inequalities for Stolarsky means and for Gini means to hold are proved, and the necessary and suffcient conditions for some companion inequalities for bivariate means to hold are given, which unify, generalize and improve known results.

#### Complete monotonicity involving some ratios of gamma functions

In this paper, by using the properties of an auxiliary function, we mainly present the necessary and sufficient conditions for various ratios constructed by gamma functions to be respectively completely and logarithmically completely monotonic. As consequences, these not only unify and improve certain known results including Qi’s and Ismail’s conclusions, but also can generate...

#### On approximating the error function

In the article, we present the necessary and sufficient condition for the parameter p on the interval ( 7 / 5 , ∞ ) such that the function x → erf ( x ) / B p ( x ) is strictly increasing (decreasing) on ( 0 , ∞ ) , and find the best possible parameters p, q on the interval ( 7 / 5 , ∞ ) such that the double inequality B p ( x ) < erf ( x ) < B q ( x ) holds for all x > 0 , where...

#### Monotonicity of a mean related to polygamma functions with an application

Let ψ n = ( − 1 ) n − 1 ψ ( n ) ( n = 0 , 1 , 2 , … ), where ψ ( n ) denotes the psi and polygamma functions. We prove that for n ≥ 0 and two different real numbers a and b, the function x ↦ ψ n − 1 ( ∫ a b ψ n ( x + t ) d t b − a ) − x is strictly increasing from ( − min ( a , b ) , ∞ ) onto ( min ( a , b ) , ( a + b ) / 2 ) , which generalizes a well-known result. As an...

#### Necessary and sufficient conditions for the two parameter generalized Wilker-type inequalities

In the article, we provide the necessary and sufficient conditions for the parameters α and β such that the generalized Wilker-type inequality 2 β α + 2 β ( sin x x ) α + α α + 2 β ( tan x x ) β − 1 > ( < ) 0 holds for all x ∈ ( 0 , π / 2 ) . MSC: 26D05, 33B10.

#### Monotonicity and absolute monotonicity for the two-parameter hyperbolic and trigonometric functions with applications

In this paper, we present the monotonicity and absolute monotonicity properties for the two-parameter hyperbolic and trigonometric functions. As applications, we find several complete monotonicity properties for the functions involving the gamma function and provide the bounds for the error function. MSC: 33B10, 33B15, 33B20, 26A48, 26D07.

#### Monotonicity of the incomplete gamma function with applications

In the article, we discuss the monotonicity properties of the function x → ( 1 − e − a x p ) 1 / p / ∫ 0 x e − t p d t for a , p > 0 with p ≠ 1 on ( 0 , ∞ ) and prove that the double inequality Γ ( 1 + 1 / p ) ( 1 − e − a x p ) 1 / p < ∫ 0 x e − t p d t < Γ ( 1 + 1 / p ) ( 1 − e − b x p ) 1 / p holds for all x > 0 if and only if a ≤ min { 1 , Γ − p ( 1 + 1 / p ) } and b ≥ max { 1...

#### Monotonicity and inequalities involving the incomplete gamma function

In the article, we deal with the monotonicity of the function x → [ ( x p + a ) 1 / p − x ] / I p ( x ) on the interval ( 0 , ∞ ) for p > 1 and a > 0 , and present the necessary and sufficient condition such that the double inequality [ ( x p + a ) 1 / p − x ] / a < I p ( x ) < [ ( x p + b ) 1 / p − x ] / b for all x > 0 and p > 1 , where I p ( x ) = e x p ∫ x ∞ e − t p d t is...

#### Monotonicity of the ratio for the complete elliptic integral and Stolarsky mean

In the article, we prove that the function r ↦ E ( r ) / S 9 / 2 − p , p ( 1 , r ′ ) is strictly increasing on ( 0 , 1 ) for p ≤ 7 / 4 and strictly decreasing on ( 0 , 1 ) for p ∈ [ 2 , 9 / 4 ] , where r ′ = 1 − r 2 , E ( r ) = ∫ 0 π / 2 1 − r 2 sin 2 ( t ) d t is the complete elliptic integral of the second kind, and S p , q ( a , b ) = [ q ( a p − b p ) / ( p ( a q − b q...

#### On approximating the modified Bessel function of the first kind and Toader-Qi mean

In the article, we present several sharp bounds for the modified Bessel function of the first kind I 0 ( t ) = ∑ n = 0 ∞ t 2 n 2 2 n ( n ! ) 2 and the Toader-Qi mean T Q ( a , b ) = 2 π ∫ 0 π / 2 a cos 2 θ b sin 2 θ d θ for all t > 0 and a , b > 0 with a ≠ b . MSC: 33C10, 26E60.

#### A Sharp Lower Bound for Toader-Qi Mean with Applications

October 2015; Revised 10 December 2015; Accepted 24 December 2015 Academic Editor: Kehe Zhu Copyright © 2016 Zhen-Hang Yang and Yu-Ming Chu. This is an open access article distributed under the Creative

#### A Sharp Lower Bound for Toader-Qi Mean with Applications

October 2015; Revised 10 December 2015; Accepted 24 December 2015 Academic Editor: Kehe Zhu Copyright © 2016 Zhen-Hang Yang and Yu-Ming Chu. This is an open access article distributed under the Creative

#### Lazarević and Cusa type inequalities for hyperbolic functions with two parameters and their applications

In the article, we establish several Lazarević and Cusa type inequalities involving the hyperbolic sine and cosine functions with two parameters. As applications, we find some new bounds for certain bivariate means. MSC: 26D05, 26D07, 33B10, 26E60.

#### Improvements of the bounds for Ramanujan constant function

In the article, we establish several inequalities for the Ramanujan constant function R ( x ) = − 2 γ − ψ ( x ) − ψ ( 1 − x ) on the interval ( 0 , 1 / 2 ] , where ψ ( x ) is the classical psi function and γ = 0.577215 ⋯ is the Euler-Mascheroni constant. MSC: 33B15, 26D07.

#### Generalized Wilker-type inequalities with two parameters

In the article, we present certain p , q ∈ R such that the Wilker-type inequalities 2 q p + 2 q ( sin x x ) p + p p + 2 q ( tan x x ) q > ( < ) 1 and ( π 2 ) p ( sin x x ) p + [ 1 − ( π 2 ) p ] ( tan x x ) q > ( < ) 1 hold for all x ∈ ( 0 , π / 2 ) . MSC: 26D05, 33B10.

#### Inequalities for certain means in two arguments

In this paper, we present the sharp bounds of the ratios U ( a , b ) / L 4 ( a , b ) , P 2 ( a , b ) / U ( a , b ) , N S ( a , b ) / P 2 ( a , b ) and B ( a , b ) / N S ( a , b ) for all a , b > 0 with a ≠ b , where L 4 ( a , b ) = [ ( b 4 − a 4 ) / ( 4 ( log b − log a ) ) ] 1 / 4 , U ( a , b ) = ( b − a ) / [ 2 arctan ( ( b − a ) / 2 a b ) ] , P 2 ( a , b ) = [ ( b 2 − a 2...

#### On approximating Mills ratio

In the article, we present several sharp bounds for the Mills ratio R ( x ) = e x 2 / 2 ∫ x ∞ e − t 2 / 2 d t ( x > 0 ) in terms of the functions I a ( x ) = a / [ x 2 + 2 a + ( a − 1 ) x ] and J ( x ) = a / [ x 2 + 2 a 2 / π + 2 a x / π ] with parameter a > 0 . MSC: 60E15, 26A48, 26D15.

#### Optimal power mean bounds for the second Yang mean

In this paper, we present the best possible parameters p and q such that the double inequality M p ( a , b ) < V ( a , b ) < M q ( a , b ) holds for all a , b > 0 with a ≠ b , where M r ( a , b ) = [ ( a r + b r ) / 2 ] 1 / r ( r ≠ 0 ) and M 0 ( a , b ) = a b is the rth power mean and V ( a , b ) = ( a − b ) / [ 2 sinh − 1 ( ( a − b ) / 2 a b ) ] is the second Yang mean. MSC: 26E60.