These drugs are available legally only by prescription, to treat conditions that occur when the body produces abnormally low amounts of testosterone, such as delayed puberty and some types of impotence. They are also used to treat body wasting in patients with AIDS and other diseases that result in loss of lean muscle mass. Abuse of anabolic steroids, however, can lead to serious health problems, some irreversible.

To understand why, just think about how heat is conducted through the air. It is carried via molecules, which constantly collide with each other and scatter the heat in all directions—forwards, sideways and even backwards. That fundamental inefficiency makes conductive heat relatively sluggish (radiant heat, by comparison, can travel at light speed as infrared radiation). The same sluggishness holds for heat moving through a solid. Here, phonons (packets of acoustic vibrational energy) carry the heat much like molecules in the air, allowing it to scatter in all directions and slowly disperse. “It's a little bit like, if you take a drop of food coloring and put it into water, it spreads,” says Keith Nelson, Duncan’s advisor at MIT. “It doesn’t just move straight as an arrow away from where you put the drop.” But that is precisely what Duncan’s experiment suggested. In second sound, the backscattering from phonons is heavily suppressed, allowing heat to shoot forward. “That’s the way wavelike motion behaves,” Nelson says. “If you’re in a pool and you launch a water wave, it will leave where you are.… But it’s just not normal for heat to behave that way.”


A drug is addicting if it causes compulsive, often uncontrollable drug craving, seeking, and use, even in the face of negative health and social consequences. Marijuana meets this criterion. More than 120,000 people enter treatment per year for their primary marijuana addiction. In addition, animal studies suggest marijuana causes physical dependence, and some people report withdrawal symptoms.
Text to speech enables brands, companies, and organizations to deliver enhanced end-user experience, while minimizing costs. Whether you’re developing services for website visitors, mobile app users, online learners, subscribers or consumers, text to speech allows you to respond to the different needs and desires of each user in terms of how they interact with your services, applications, devices, and content.
Laughing gas is available several forms, one being the medical form which is produced to be used as an anaesthetic and is therefore subject to pharmaceuticals law. A second, less pure form of laughing gas is for commercial use and is commonly used to tune engines. This less pure form may often contain other chemicals or gases such as methyl nitrate which can lead to oxygen deficiency in the human body. Laughing gas can also be purchased in cartridges that can be used to make whipped cream.
Laughing gas is available several forms, one being the medical form which is produced to be used as an anaesthetic and is therefore subject to pharmaceuticals law. A second, less pure form of laughing gas is for commercial use and is commonly used to tune engines. This less pure form may often contain other chemicals or gases such as methyl nitrate which can lead to oxygen deficiency in the human body. Laughing gas can also be purchased in cartridges that can be used to make whipped cream.
تتألف الموجة الصوتية أو الأمواج الصوتية في أي وسط من حركة اهتزازية حركة اهتزازية سريعة للجزيئات التي تألف الوسط. فحركة إحدى جزيئات الوسط تؤدي إلى اضطراب الجزيئات المجاورة، وهذه بدورها تقوم بنفس العمل، وهكذا دواليك، بحيث أن موجة من الاضطراب تعبر الوسط ابتداء من نقطة الحركة الأولى. وعندما تهتز الشوكة الرنانة في الهواء، فإن حركة الشعبة المهتزة إلى الأمام تضغط الهواء المجاور. إلا أنه سرعان ماتعود هذه المنطقة المنضغطة من الهواء إلى حالتها الاعتيادية بفضل الخاصة المطاطية للهواء وعلى حساب انضغاط المناطق المجاورة، بحيث أن موجة من الضغط الزائد تنتشر ابتداء من الشعبة المهتزة من الشوكة الرنانة، وبنفس الطريقة فإن حركة الشعبة المهتزة إلى الخلف تولد موجة من الضغط الناقص أو التخلخل.
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