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"Ge, Hua"
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الصين فى عشر كلمات
يسلط الكاتب أضواء كاشفة على تعاظم سرعة \"المعجزة الاقتصادية\" في الصين، ويبدو أن كل شي تغير في مثل لمح البصر، وكان ذلك على غرار القفز الطويل حيث جعل الصينيين يقفزون من عصر العوز المادي إلي عصر البذخ والتبذير، ومن عصر السياسة في المقام الأول إلى عصر المال أولا، ومن عصر غريزة القمع إلي عصر الاندفاع والتهور والانغماس في اللهو والمجون، لقد انقضي ثلاثون عاما وأكثر كأنها قفزة في الهواء. وكأن كاتبنا، الذي عاش في كنف التغيرات الهائلة والتحولات الكبري التي اجتاحت الصين في نصف القرن الأخير كان كالسمكة التي تسكن بحورا عميقة تروح وتجئ وسط الغموض تغزل طريقها بين سيقان أعشاب ضخمة فوق أماكن تضوي فيها أشعة الشمس، وتغوص إلى أسفل وأسفل حتى تصل إلي ظلام بارد عميق غامض، وفجأة تنطلق إلى السطح وتلهو فوق الأمواج التي تداعبها الريح، يمسك كاتبنا مبضعه الأدبي-النفسي، ويوضح نقطة سيكولوجية مهمة كأنه الطبيب النفسي الذي يشرح داخل وأعماق النفس الإنسانية، ويقول : إن عصر الكبت المتطرف بعد أن شهد التغيرات الاجتماعية الهائلة من المحتوم أن ينبثق منه عصر آخر مغاير تماما من التسامح المتطرف، وذلك يشبه اللعب على الأرجوحة حيث عندما ينخفض أحد طرفيها، فمن المؤكد أن يعلو كثيرا الطرف الآخر المتأرجح. ولا ينفك يحذر من مغبة أن الحياة الاجتماعية غير المتوازنة من المؤكد أن تجلب الأحلام غير المتوازنة التي بدروها تفرز أحلام التطرف والسعي وراء النجاحات السريعة والقفز فوق المراحل.
Book
Exceptional figure of merit achieved in boron-dispersed GeTe-based thermoelectric composites
GeTe is a promising p-type material with increasingly enhanced thermoelectric properties reported in recent years, demonstrating its superiority for mid-temperature applications. In this work, the thermoelectric performance of GeTe is improved by a facile composite approach. We find that incorporating a small amount of boron particles into the Bi-doped GeTe leads to significant enhancement in power factor and simultaneous reduction in thermal conductivity, through which the synergistic modulation of electrical and thermal transport properties is realized. The thermal mismatch between the boron particles and the matrix induces high-density dislocations that effectively scatter the mid-frequency phonons, accounting for a minimum lattice thermal conductivity of 0.43 Wm
−1
K
−1
at 613 K. Furthermore, the presence of boron/GeTe interfaces modifies the interfacial potential barriers, resulting in increased Seebeck coefficient and hence enhanced power factor (25.4 μWcm
−1
K
−2
at 300 K). Consequently, we obtain a maximum figure of merit
Z
max
of 4.0 × 10
−3
K
−1
at 613 K in the GeTe-based composites, which is the record-high value in GeTe-based thermoelectric materials and also superior to most of thermoelectric systems for mid-temperature applications. This work provides an effective way to further enhance the performance of GeTe-based thermoelectrics.
Doping approach is a conventional method to increase ZT values of thermoelectric materials. Here, authors propose a facile strategy to enhance thermoelectric performance by mixing boron particles into GeTe-based thermoelectric materials, leading to a ZT value of 2.45 at 613 K.
Journal Article
أفكار حول تعميق الإصلاح
يناقش الكتاب سلسلة من الإيضاحات الهامة قدمها الرئيس الصيني والأمين العام للجنة المركزية للحزب الشيوعي الصيني، شي جين بينغ، وتدور حول أفكار الإصلاح وتوسيع الانفتاح على نحو شامل في الصين. يضم الكتاب أكثر من 70 وثيقة هامة على صورة كلمات شي جين بينغ وخطاباته وتعليقاته وتوجيهاته وينقسم الكتاب إلى 12 موضوعا خاصا تتضمن 274 قطعة من مقتطفات الأقوال، نشر بعضها لأول مرة.
Book
High thermoelectric efficiency realized in SnSe crystals via structural modulation
Crystalline thermoelectrics have been developed to be potential candidates for power generation and electronic cooling, among which SnSe crystals are becoming the most representative. Herein, we realize high-performance SnSe crystals with promising efficiency through a structural modulation strategy. By alloying strontium at Sn sites, we modify the crystal structure and facilitate the multiband synglisis in p-type SnSe, favoring the optimization of interactive parameters
μ
and
m
*
. Resultantly, we obtain a significantly enhanced
PF
~85 μW cm
−1
K
−2
, with an ultrahigh
ZT
~1.4 at 300 K and
ZT
ave
~2.0 among 300–673 K. Moreover, the excellent properties lead to single-leg device efficiency of ~8.9% under a temperature difference
ΔT
~300 K, showing superiority among the current low- to mid-temperature thermoelectrics, with an enhanced cooling Δ
T
max
of ~50.4 K in the 7-pair thermoelectric device. Our study further advances p-type SnSe crystals for practical waste heat recovery and electronic cooling.
Thermoelectric technology directly enables both power generation and electronic cooling. Here, the authors realize high-performance SnSe crystals with promising device efficiencies by modulating crystal and band structures.
Journal Article
تحديث الاقتصاد الصيني
في كتابه \"تحديث الاقتصاد الصيني\" يتناول تشياو جنغ عملية الإصلاح الاقتصادي في الصين خلال ثلاثة عقود تم فيها وصف التطور السريع لاقتصاد الصين ب\"المعجزة الاقتصادية\"، ولكنه وصف غير دقيق -بتعبير المؤلف- وبمعنى أكثر دقة، يعتبر التطور السريع لاقتصاد الصين مجرد عملية انتعاش اقتصادي. إنها عملية مواكبة لاقتصادات الأسواق في المناطق المتقدمة.
Book
Realizing high-ranged thermoelectric performance in PbSnS2 crystals
Great progress has been achieved in p-type SnS thermoelectric compound recently, while the stagnation of the n-type counterpart hinders the construction of thermoelectric devices. Herein, n-type sulfide PbSnS
2
with isostructural to SnS is obtained through Pb alloying and achieves a maximum
ZT
of ~1.2 and an average
ZT
of ~0.75 within 300–773 K, which originates from enhanced power factor and intrinsically ultralow thermal conductivity. Combining the optimized carrier concentration by Cl doping and enlarged Seebeck coefficient through activating multiple conduction bands evolutions with temperature, favorable power factors are maintained. Besides, the electron doping stabilizes the phase of PbSnS
2
and the complex-crystal-structure induced strong anharmonicity results in ultralow lattice thermal conductivity. Moreover, a maximum power generation efficiency of ~2.7% can be acquired in a single-leg device. Our study develops a n-type sulfide PbSnS
2
with high performance, which is a potential candidate to match the excellent p-type SnS.
Direct and reversible conversion between heat and electricity can be achieved in thermoelectric materials. Here, the authors realize high thermoelectric performance in PbSnS
2
crystals enabled by multiple bands convergence.
Journal Article
Channel-forming discharge based on the extreme value identification of sediment-carrying capacity index
Channel-forming discharge (
D
cf
) is an important parameter in river management and reservoir flood regulation. Applying the methods for calculating
D
cf
to reaches downstream reservoirs characterized by drastic changes in water and sediment conditions and long-term scouring status is difficult. Based on the riverbed-shaping principle of sediment-laden water flow, while simultaneously considering the active action of water flow and response of the riverbed, this study proposes a new method for calculating
D
cf
by identifying the extreme value of the suspended sediment-carrying capacity index. The application of this method to the middle and lower reaches of the Yangtze River showed that after the impoundment of the Three Gorges Reservoir,
D
cf
in this section was reduced by an amplitude between 2500 and 4700 m
3
/s. The results can be used to guide the operation of the Three Gorges Reservoir and the management of the middle and lower reaches of the Yangtze River, thus providing reference for other river channels downstream of the reservoir.
Journal Article
Tunable Electrical Conductivity and Simultaneously Enhanced Thermoelectric and Mechanical Properties in n‐type Bi2Te3
The recent growing energy crisis draws considerable attention to high‐performance thermoelectric materials. n‐type bismuth telluride is still irreplaceable at near room temperature for commercial application, and therefore, is worthy of further investigation. In this work, nanostructured Bi2Te3 polycrystalline materials with highly enhanced thermoelectric properties are obtained by alkali metal Na solid solution. Na is chosen as the cation site dopant for n‐type polycrystalline Bi2Te3. Na enters the Bi site, introducing holes in the Bi2Te3 matrix and rendering the electrical conductivity tunable from 300 to 1800 Scm–1. The solid solution limit of Na in Bi2Te3 exceeds 0.3 wt%. Owing to the effective solid solution, the Fermi level of Bi2Te3 is properly regulated, leading to an improved Seebeck coefficient. In addition, the scattering of both charge carriers and phonons is modulated, which ensured a high‐power factor and low lattice thermal conductivity. Benefitting from the synergistic optimization of both electrical and thermal transport properties, a maximum figure of merit (ZT) of 1.03 is achieved at 303 K when the doping content is 0.25 wt%, which is 70% higher than that of the pristine sample. This work disclosed an effective strategy for enhancing the performance of n‐type bismuth telluride‐based alloy materials. In this study, Na as the n‐type dopant is introduced in the polycrystalline Bi2Te3 material for enhancing the thermoelectric and mechanical properties. Benefitting from the synergistic optimization of electrical and thermal transport properties, a maximum ZT value of 1.03 is achieved at 303 K for the Bi2Te3‐0.25 wt% sample, which is 70% higher than that of the pristine sample.
Journal Article
Synergistically optimized electron and phonon transport in high-performance copper sulfides thermoelectric materials via one-pot modulation
Optimizing thermoelectric conversion efficiency requires the compromise of electrical and thermal properties of materials, which are hard to simultaneously improve due to the strong coupling of carrier and phonon transport. Herein, a one-pot approach realizing simultaneous second phase and Cu vacancies modulation is proposed, which is effective in synergistically optimizing thermoelectric performance in copper sulfides. Multiple lattice defects, including nanoprecipitates, dislocations, and nanopores are produced by adding a refined ratio of Sn and Se. Phonon transport is significantly suppressed by multiple mechanisms. An ultralow lattice thermal conductivity is therefore obtained. Furthermore, extra Se is added in the copper sulfide for optimizing electrical transport properties by inducing generating Cu vacancies. Ultimately, an excellent figure of merit of ~1.6 at 873 K is realized in the Cu
1.992
SSe
0.016
(Cu
2
SnSe
4
)
0.004
bulk sample. The simple strategy of inducing compositional and structural modulation for improving thermoelectric parameters promotes low-cost high-performance copper sulfides as alternatives in thermoelectric applications.
It is hard to simultaneously improve electrical and thermal properties of materials due to the strong coupling of carrier and phonon transport. Here, the authors propose a one-pot modulation strategy for simultaneously adjusting carrier and phonon transport in copper sulfids.
Journal Article
Positive definiteness of fourth-order partially symmetric tensors
In this paper, we consider the positive definiteness of fourth-order partially symmetric tensors. First, two analytically sufficient and necessary conditions of positive definiteness are provided for fourth-order two dimensional partially symmetric tensors. Then, we obtain several sufficient conditions for rank-one positive definiteness of fourth-order three dimensional partially symmetric tensors.
Journal Article