Friday, 15 February 2019

Notification for CSIR NET JUNE 2019

CSIR NET 2019 June Notification, Syllabus, Dates, Application

 CSIR NET HRDG has released official notification for JUNE 2019 Exam. CSIR NET June 2019 Applications Details, Essential Qualification required, the Last Date to Appy Online and Eligibility can be checked below. CSIR NET Exam is conducted twice in a year. CSIR NET June exam this year will be conducted on 16th June 2019. An official announcement for CSIR NET June Exam has been released by CSIR.
 
CSIR NET JUNE 2019 Exam Date, Online Application Open date & Deadline are as follows:
              
CSIR NET June 2019 Exam To Be Held On16th June 2019
CSIR NET JUNE 2019 Information Bulletin for detailed information/instructions available from19th February 2019
CSIR NET JUNE 2019 Online Application Starts From25th February 2019
Last Date to Apply For CSIR NET June 2019 Exam18th March 2019

Council of Scientific and Industrial Research
Human Resource Development Group, Examination Unit
CSIR Complex, Library Avenue, Pusa, New Delhi-110012
Joint CSIR-UGC National Eligibility Test (NET) for Junior Research Fellowship
(JRF) and for Lectureship (LS)
NOTIFICATION No.10-2(5)/2019(i) – E.U.II

CSIR has scheduled the Joint CSIR-UGC Test tentatively on Sunday, 16th June 2019
for determining the eligibility of Indian Nationals for the award of Junior Research
Fellowships (JRF) and for determining eligibility for appointment as Lecturer (LS) in
the areas of Chemical Sciences, Earth, Atmospheric, Ocean and Planetary Sciences,
Life Sciences, Mathematical Sciences, Physical Sciences. The award of Junior
Research Fellowship to the successful eligible candidates will depend on their finding
admission/placement in a University/ National laboratory/ Institution of higher learning
and research, as applicable.

Essential Qualification : M.Sc or equivalent degree/ Integrated BS-MS/BS-4
years/BE/BTech/BPharma/MBBS with at least 55% marks for General (UR) and OBC
candidates and 50% for SC/ST, Persons with Disability (PWD) candidates;
Candidates enrolled for M.Sc or having completed 10+2+3 years of the above
qualifying examination as on the closing date of online submission of application form,
are also eligible to apply in the above subject under the Result Awaited (RA) category
on the condition that they complete the qualifying degree with requisite percentage of
marks within the validity period of two years to avail the fellowship from the effective
date of award (Such candidates will have to submit the attestation form duly certified
by the Head of the Department/Institute from where the candidate is appearing or has
appeared);
B. Sc (Hons) or equivalent degree holders or students enrolled in Integrated MS-Ph.D
program with at least 55% marks for General (UR) and OBC candidates; 50% marks
for SC/ST, Persons with Disability (PwD) candidates are also eligible to apply.
Candidates with a bachelor’s degree will be eligible for CSIR fellowship only after getting
registered/enrolled for Ph. D/Integrated Ph. D program within the validity period of two
years.
Candidates possessing only Bachelor’s degree shall not be eligible for Lectureship;
Specification of degrees (whether Bachelor’s or Master’s) as notified by the UGC in its
Gazette Notification No. F. 5-1/2013 (CPP-II) dated 5th July 2014 and as amended
from time to time, shall apply;
The eligibility for lectureship of NET qualified candidates will be subject to fulfilling the
criteria laid down by UGC. Ph. D degree holders who have passed Master’s degree
prior to 19th September 1991, with at least 50% marks are eligible to apply for
Lectureship only.

Examination Fee : General: Rs.1000/-, OBC (Non-Creamy Layer): Rs.500/-, and
SC/ST/PwD: Rs. 250/-.Other Backward Class (OBC) candidate whose caste is not listed in the Central
List and/or who do not belong to OBC (Non-Creamy Layer), though his/her
caste is listed in the central list, shall apply as ‘General’ candidate and is required
to pay Examination fee @ Rs. 1000/-.
Candidates applying for the Examination are required to use payment gateway facility
to deposit their Examination fee only through Credit Card or Debit Card or Net Banking.
Candidates are not required to pay any transaction charges for using the payment gateway
facility.
SessionsSubjectTimingsMarksDuration
Morning SessionLife Sciences & Physical Sciences9.00 AM – 12.00 PM200 3 Hours
Afternoon SessionChemical Sciences, Mathematical Session Sciences, Earth, Atmospheric, Ocean and Planetary Sciences2.00 PM – 5.00 PM2003 Hours

The subject-wise session and timing of the Test is liable to be changed at the discretion
of CSIR, depending on the number of candidates in each subject.

 CLICK ON BELOW LINKS TO KNOW MORE πŸ‘‡



 Interested eligible candidates may visit CSIR-HRDG website (www.csirhrdg.res.in)
and see the Information Bulletin for detailed information/instructions from 19.02.2019.


Monday, 11 February 2019

List of Universities and Institutes offering different Courses in Microbiology


More than a few colleges as well as other educational institutions are there in country that provides students with many postgraduate as well as undergraduate level courses in microbiology. As to get admitted into such courses, desirous students will need to appear for an entrance exam. This exam can be set by an individual university or can be set in the national level.

      List of Microbiology Entrance Exams
  • The Indian Institute of Science (IISc) Entrance Exam
  • Indian Institute of Technology Entrance Exam (IIMK)
  • Mahatma Gandhi University : Faculty of Applied Science Entrance Exam
  • University of Calicut Microbiology Entrance Exam
  • University of Kerala : Faculty of Science Microbiology Entrance Exam
  • Aligarh Muslim University Microbiology Entrance Exam
  • Assam University Microbiology Entrance Exam
  • Banaras Hindu University Microbiology Entrance Exam
  • Goa University Microbiology Entrance Exam
  • Guru Nanak Dev University M.Sc Microbiology Entrance Exam
  • Himachal Pradesh University Shimla - Microbiology Entrance Test
  • Lovely Professional University Microbiology Entrance Exam
  • M.Sc (Biotechnology)& IIT JAM Entrance Exams
  • Mahatma Gandhi University Microbiology Entrance Exam
  • Manipal Academy of Higher Education Microbiology Entrance Exam
  • Osmania university Microbiology Entrance Exam
  • University of Calcutta Microbiology Entrance Exam
  • University of Mumbai Microbiology Entrance Exam
  • University of Pune Microbiology Entrance Exam

    List of Courses available in Microbiology.
  • B.Sc. Clinical Microbiology
  • B.Sc. Industrial Microbiology
  • B.Sc. Medical Microbiology
  • B.Sc. Microbiology
  • B.Sc. Microbiology and Microbial Technology
  • Diploma in Microbiology
  • M.D. Microbiology
  • M.Phil. Microbiology
  • M.S. Stem Cell Biology
  • M.Sc. Applied Microbiology
  • M.Sc. Clinical Microbiology
  • M.Sc. Microbiology
  • M.Sc. Microbiology (Integrated)
  • Ph.D. Microbiology


Application Procedure for the Microbiology Course
The cost of application forms for these exams will range from Rs. 500/- to Rs. 2000/-. Students who wish to appear for the exams can procure the application from the counter of the concerned institution or download it from the official website of the same.




πŸ††πŸ…΄ πŸ††πŸ…ΎπŸ†„πŸ…»πŸ…³ πŸ…»πŸ…ΈπŸ…ΊπŸ…΄ πŸ†ƒπŸ…Ύ πŸ…·πŸ…΄πŸ…°πŸ† πŸ…΅πŸ†πŸ…ΎπŸ…Ό πŸ†ˆπŸ…ΎπŸ†„.... πŸ†ƒπŸ…·πŸ…°πŸ…½πŸ…Ί πŸ†ˆπŸ…ΎπŸ†„

Leave a Comment .     
  Subscribe for more

Saturday, 9 February 2019

List of Life Sciences PhD Entrance Exams across India

List of PhD Entrance Exams



Postgraduates in any streams can pursue the PhD course in the related fields so as to carry out research and development in the concerned areas. The PhD entrance exams conducted may vary with Universities. Only Masters’ degree holders’ will be eligible to appear for the test. Most of the Universities require 55% marks in the qualifying course. The percentage requisites may vary with institutes.

Given beneath is the list of PhD entrance exams carried out by various Universities and institutes.

List of PhD Entrance Exams
  • UGC NET exam
  • Symbiosis PhD Entrance Examination
  • AIMA PhD Entrance Exam
  • JNU PhD Entrance Exam
  • NIPER PhD Entrance Exam
  • Alagappa University PhD Entrance Exam
  • Kurukshetra University PhD Entrance Exam
  • University of Hyderabad PhD Entrance Exam
  • GTU PhD Entrance Exam
  • National Brain Research Centre, PHD Entrance Exam
  • PhD Examination: Mohan Lal Sukhadia University, Udaipur
  • BR Ambedkar Open University PhD Entrance Exam
  • BITS Pilani PhD Entrance Examination
  • ICT Mumbai PhD Entrance Exam
  • Indian Agricultural Research Institute PhD Entrance Exam
  • Osmania University PhD Entrance Exam
  • AIIMS PhD Entrance Exam
  • IISC PhD Entrance Exam
  • PhD Entrance Exam of NMIMS University Mumbai
  • Chaudhary Devi Lal University (CDLU) Sirsa PhD Entrance Exam
  • NDRI PhD entrance exam
  • Kerala University PhD Entrance Exam
  • Punjab Technical University PhD Entrance Exam
  • Anna University Center for Research PhD Entrance Test
  • Annamalai University PhD Admission test
  • Apeejay Stya University PhD Admission test
  • Asia University Madurai PhD Admission test
  • Atal Bihari Vajpayee Indian Institute of Information Technology and Management Gwalior PhD Admission Test
  • Babasaheb Bhimrao Ambedkar University Lucknow - PhD Admissions Test
  • Bhabha Atomic Research Centre (BARC) PhD Admission Test
  • Bharathiar University Coimbatore - PhD Part-Time Admissions Test
  • Bhatiya Shiksha Parishad Uttar Pradesh - PhD Admissions Test
  • Central Institute of Medicinal and Aromatic Plants Lucknow PhD Admission Test
  • Centre for Development Studies Thiruvananthapuram PhD Admission Test
  • Chennai Mathematical Institute - Ph.D Admission Test
  • Defense Institute of Advanced Technology Pune PhD Admission Test
  • Delhi Technological University Delhi PhD Admission Test
  • Dr Harisingh Gour Vishwavidyalaya Sagar Madhya Pradesh PhD Admissions Test
  • Dr Yashwant Singh Parmar University of Horticulture and Forestry Nauni Solan - PhD Admissions Test
  • Dravidian University Srinivasavanam Kuppam Andhra Pradesh - PhD Admission Test
  • Faculty of Education University of Delhi PhD Admission Test
  • GITAM University Vishakhapatnam PhD Admissions Test
  • Guru Angad Dev Veterinary and Animal Sciences University Ludhiana - PhD Admission Test
  • Guru Gobind Singh Indraprastha University Delhi PhD Admission Test
  • Himachal Pradesh University Shimla PhD Admission Test
  • IFTM University Moradabad PhD Admission Test
  • IISER Indian Institute of Science Education and Research Mohali PhD Admission Test
  • IIST Indian Institute of Space Science and Technology Thiruvananthapuram PhD Admission Test
  • Indian Institute of Crop Processing Technology Thanjavur - PhD Admission Test
  • Indian Institute of Information Technology, Design and Manufacturing Jabalpur IIITDM PhD Admission Test
  • Indian Institute of Technology (IIT) Guwahati - PhD Admissions Test
  • Indian School of Mines Dhanbad PhD Admission Test
  • Indian Veterinary Research Institute Bareilly PhD Admission Test
  • Indira Gandhi Institute of Development Research Mumbai PhD Admission Test
  • Indraprashtha Institute of Information Technology (IIIT) Delhi - PhD Admission Test
  • Institute for Financial Management and Research Chennai PhD Entrance Test
  • Institute of Bio resources and Sustainable Development (IBSD) Imphal - PhD Admissions Test
  • Institute of Genomics and Integrative Biology Delhi PhD Admission Test
  • Institute of Management Technology Ghaziabad - PhD Admissions Test
  • International Centre for Genetic Engineering & Biotechnology (ICGEB) New Delhi PhD Admission Test
  • Jamia Hamdard New Delhi PhD Admission Test
  • Jamia Millia Islamia New Delhi - PhD Admission Test
  • Jaypee Institute of Information Technology (JIIT) Noida PhD Admission Test
  • Kalasalingam University PhD Admission Test
  • Lingaya University Faridabad - PhD Admission Test
Exam Pattern of the PhD Entrance Exam
The PhD entrance test mainly comprises of two parts. One will be a Research Aptitude test, which consists of questions numerical ability, language proficiency and logical reasoning. The second part will be a subject specific test, which may contain multiple choice and explanatory type questions. In the second part, questions will be on the technical subjects of the qualifying course.
Application Procedure for the PhD Course
Applicants can contact the official address of the University, which they wish to study the course for procuring PhD entrance exam form along with prospectus. After correctly filling the forms, applicants have to send it to the University official address prior to the last date. They must also attach pertinent credentials mentioned in the brochure along with the forms. Some Universities also allow online submission of forms.



Do you have any question? Please ask

Do you know the Differences between Prokaryotes and Eukaryotes ?


The 36 differences between Prokaryotes and Eukaryotes 



The major differences between Prokaryotes and Eukaryotes are summarized in the following table:
.
Sl. No.ProkaryotesEukaryotes
1‘pro’ = pre, ‘karyon’= nucleus‘eu’ = true, ‘karyo’ = nucleus
2Originated about 3.5 billion years agoOriginated about 1.2 billion years ago
3Primitive formsAdvanced forms
4Usually unicellular organizationUsually multicellular organization
5Incipient nucleus, true nucleus absentTrue nucleus present
6Small cell size, usually 1 – 10 Β΅mLarger cell size, usually 5 – 100 Β΅m, sometimes very large and macroscopic
7Membrane bounded organelles such as nucleus, mitochondria, Golgi bodies, chloroplasts, lysosome, peroxisomes, ER etc. are absentMembrane bounded organelles present. Majority of organelles have single or double membrane system
8Genetic material consists of single chromosomeGenetic materials usually consists of more than one chromosomes
9Genetic material is freely distributed in the central portion of the cell (nucleoplasm)Genetic material is located in the nucleus
10Chromosome with covalently closed circular DNA (ccc DNA)Chromosome with linear DNA
11Cell division by fission or budding, Mitosis and Meiosis completely absentCell division by mitosis and meiosis
12Nucleolus absentA well-developed nucleolus present
13Ribosome 70S typeRibosome 80S type
14Two subunits of ribosomes are 50S large subunit and 30S small subunitTwo subunits of ribosome are 60S larger subunit and 40S smaller subunit
15DNA is naked, not associated with histone proteinsDNA is wrapped around histone proteins
16Endoplasmic reticulum absent and hence protein synthesizing ribosome freely distributed in the cytoplasmEndoplasmic reticulum present, protein synthesizing ribosome usually attached to endoplasmic reticulum
17Internal membrane system scarce. If present, associated with respiration and photosynthesisInternal membrane system well developed. Cell organelles are surrounded by single or double membranes
18Flagella with simple organizationFlagella (if present) is very complex with 9 + 2 arrangement of microtubules
19Microtubules absent in flagellaMicrotubules present in flagella
20Flagella extracellular and not enclosed by cell surface membraneFlagella intracellular and surrounded by cell surface membrane
21Cell wall is composed of muco-polysaccharidesCell wall (if present) composed of cellulose (in plants) and chitin (in fungi). Cell wall absent in animal cells
22Organisms haploid, contain only a single copy of genomeOrganisms usually diploid very rarely polyploids, contains two copies of genome, one from each parent
23Plasmid (extra-chromosomal genetic materials) usually presentPlasmids absent, however mitochondria and chloroplasts are autonomous with its own genetic materials
24Cytoskeleton system absentCytoskeleton system well developed
25Sexual reproduction absentSexual reproduction present
26Processes like transformation conjugation and, transduction present for genetic material exchangeAll such processes completely absent, and genetic exchange occurs through sexual reproduction
27Respiration is by mesosomesRespiration is by mitochondria
28Chloroplasts and mitochondria absentChloroplasts and mitochondria present, both are double membrane bounded and autonomous with its own genetic materials
29Photosynthesis takes place in the membrane system of cytoplasmPhotosynthesis takes place in chloroplast. Chloroplasts contains membrane stacks into lamella or stroma
30Nitrogen fixing capacity is present in some formsNitrogen fixing capacity is completely absent. None of the eukaryotic cells is known to processes nitrogen fixing ability both in plants and animals
31Endocytosis and phagocytosis completely absentEndocytosis and phagocytosis is present in some animals cells
32Cytoplasmic movement (cyclosis) absentCyclosis present
33Well-developed intracellular and extracellular communication system absentCommunication system is well developed and advanced
34Cell cycle duration about 20 – 60 minutesHighly varies, rapidly dividing cells the cell cycle is ~ 24 hours
35Regulatory mechanisms of DNA relatively simpleRegulatory mechanism highly complex
36Transcription and translation are continuous process and occurs simultaneously in the cytoplasmThey are separate processes, transcription occurs in the nucleus whereas translation occurs in the cytoplasm

We would Love to hear from you!!! Leave a comment.....

Do you know these facts about Microscope ?

FUN FACTS ABOUT THE HISTORY OF THE MICROSCOPE



The earliest microscopes were known as “flea glasses” because they were used to study small insects.

A father-son duo, Zacharias and Han Jansen, created the first compound microscope in the 1590s.

Anton van Leeuwenhoek created powerful lenses that could see teeming bacteria in a drop of water.

Robert Hooke discovered cells by studying the honeycomb structure of a cork under a microscope.

Marcello Marpighi, known as the father of microscopic anatomy, found taste buds and red blood cells.

Robert Koch used a compound microscope to discover tubercle and cholera bacilli.

German engineer Carl Zeiss revolutionized the quality of lenses in the 19th century.

The smallest object observed through a light microscope was 500 nanometers long.

In 2008 the TEAM 0.5 debuted. It is the world’s most powerful transmission electron microscope and is capable of producing images half a ten-billionth of a meter.

Researchers used microscopes in 2013 to demonstrate how life could have started.





We would like to hear from you ! Leave a comment.

Tuesday, 5 February 2019

MCQs in Biochemistry


Get a perfect set of questions in biochemistry . Best practice questions for Life Science aspirants.


Download : https://drive.google.com/open?id=1lMbBWvFKYL6mU-cknc2Pd0-qhq-2il29






  THANK YOU VISIT AGAIN



Monday, 4 February 2019

CSIR NET Preparation tips

CSIR NET Preparation Tips

 Essential Things for Better Start!
The below-given points can also be considered as pre-requisites before beginning up to the actual subject-wise preparation. Please check out the essential resources which you need to gather before starting the exam preparation.
Review the Complete CSIR NET Syllabus and list up all the topics on a paper.
While choosing the study resources, make sure it covers the complete syllabus.
Understand the CSIR NET Exam Pattern and set your targeted score to bag up the exam qualification.

·         Plan a study schedule to manage your time effectively during the exam preparation.
·         Spend at least 5 hours on your studies daily and allow 1 hour extra for revision.
·         Take Important Topics at first. And as soon as you complete a topic, revise it instantly!
·         Also perform the combined revision of the topics which you studied during the whole day long, before going to sleep at night.
·         Utilize Morning Hours on those topics that you find difficult to learn and understand.
·         Noon Hours should be spent on the topics which can be solved with the help of short tricks and methods.
·         Try to cover your maximum portion in Morning and Noon Hours and dedicate evening hours for refining your performance.

The best way to polish up your skills and improve your performance is to solve CSIR NET Previous Years Question Papers.
The exam syllabus is vast and covering every single topic is very difficult for the aspirants.
Start taking CSIR NET Online Test Series with 1 month left for the exam, so that, you can self-assess your performance and put your efforts towards improving it.
For better learning practices, avoid cramming and focus more on understanding their actual meanings and methods.
Tip: Remember that ‘Speed and Accuracy’ are two essential skills to score well in any competitive Exam!

WHEN YOU FEEL LIKE QUITTING , REMEMBER WHY YOU STARTED






SUBSCRIBE THROUGH EMAIL......

Reference books for various Life Science Examinations

  Books to refer for various LIFE SCIENCE examinations  

Notch up a good score in Life Science examinations you need a proper preparation strategy and best study material.
Here are some reference books of life sciences which help you to prepare well for various Life Science exams.

 Biochemistry

  1. Lehninger Principles of Biochemistry – David L. Nelson and Michael M. Cox
  2. Biochemistry: International Edition – Stryer, Berg and Tymoczko
  3. Principles of Biochemistry – Voet, Pratt and Voet
  4. ENZYMES: Biochemistry, Biotechnology, Clinical Chemistry, 2/E – Trevor Palmer and Philip Bonner

Genetics

  1. Principles of Genetics – D. Peter Snustad, Michael J. Simmons
  2. Genetics: Principles and Analysis – Daniel L. Hartl and Elizabeth W. Jones
  3. Genetics – BD Singh

Cell and Molecular Biology

  1. The Cell: A Molecular Approach – Geoffrey M. Cooper
  2. Cell and Molecular Biology: Concepts and Experiments – Gerald Karp
  3. Molecular Biology of the Cell – Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, and Peter Walter
  4. Cell And Molecular Biology / 8th Edn. – Robertis De
  5. Molecular Cell Biology: International Edition – Harvey Lodish, Arnold Berk, Chris A. Kaiser, Monty Krieger, Anthony Bretscher, Hidde Ploegh, Angelika Amon, and Matthew P. Scott
  6. Molecular Biology of the Gene – James D. Watson, Tania A. Baker, Stephen P. Bell, Alexander Gann, Michael Levine, and Richard Losick

Immunology

  1. Kuby Immunology
  2. Essential Immunology – Ivan M. Roitt | Roitt’s Essential Immunology: Includes Desktop Edition – Peter J. Delves, Seamus J. Martin, Dennis R. Burton, Ivan M. Roitt

Developmental Biology

  1. Developmental Biology – Scott F. Gilbert
  2. Principles of Development 5e – Lewis Wolpert

Plant Physiology

  1. Plants Physiology – Lincoln Taiz and Eduardo Zeiger
  2. Plant Physiology – Ross and Salisbury

Animal Physiology

  1. Essentials of Animal Physiology – Rastogi
  2. Ganong’s Review of Medical Physiology
  3. Schaums Outline of Human Anatomy and Physiology, Third Edition (Schaums Outline Series)

Ecology

  1. Basic Ecology: Fundamentals of Ecology – Eugene P. Odum
  2. Ecology and Environment –  PD Sharma
  3. Ecology: Principles And Applications – JL Chapman and MJ Reiss

Evolution

  1. Organic Evolution (Evolutionary Biology) – Veer Bala Rastogi

Methods in Biology

  1. Principles and Techniques of Biochemistry and Molecular Biology – Wilson and Walker
  2. Biophysical Chemistry (Principles and Techniques) – Upadhyay

Recombinant DNA Technology

  1. Principles of Gene Manipulation and Genomics – Sandy B. Primrose and Richard Twyman
  2. Molecular Cloning: A Laboratory Manual – Joseph Sambrook and David Russell
  3. Gene Cloning and DNA Analysis – TA Brown
  4. Molecular Biotechnology: Principles and Applications of Recombinant DNA – Bernard R. Glick and Jack J. Pasternak

"Great books help you understand , and

they help you understood...." 

 

 

CLICK πŸ‘‰   SUBSCRIBE THROUGH EMAIL TO STAY UPDATED 

πŸ˜„  COMMENTS AND SUGGESTIONS ARE ALWAYS WELCOME  πŸ˜„


BOOKS WILL BE UPLOADED SOON


 

Saturday, 2 February 2019

Previous years CSIR NET Question Papers (From 2008)

Previous years CSIR NET Question Papers (From 2008)




PAPER
LINK
CSIR NET QUESTION PAPER 2007
CSIR NET QUESTION PAPER 2008
CSIR NET QUESTION PAPER 2009
CSIR NET QUESTION PAPER 2010
CSIR NET QUESTION PAPER 2012
CSIR NET QUESTION PAPER 2013
CSIR NET QUESTION PAPER 2014
CSIR NET QUESTION PAPER JUN 2015
CSIR NET QUESTION PAPER DEC 2015
CSIR NET QUESTION PAPER JUN 2016
CSIR NET QUESTION PAPER DEC 2016
CSIR NET QUESTION PAPER JUN 2017
CSIR NET QUESTION PAPER DEC 2017
CSIR NET QUESTION PAPER JUN 2018
CSIR NET QUESTION PAPER DEC 2018












































 


**PLEASE LEAVE A COMMENT                         **SUGGESTIONS ARE ALWAYS WELCOME

  Buy Headphones